Guide

A simple SKU system for resellers (and why it makes fulfillment easier)

A SKU is just a short code that identifies one item or one type of item. A good code means you never hunt for what you sold.

General information only, not legal or tax advice. I am not a CPA or an attorney.

What a SKU is

SKU stands for stock keeping unit. It is a short, unique code you assign to each item you hold, such as JW-2610-014. You pick the format. The same code goes on the item, in your spreadsheet and in the listing.

Why it helps fulfillment

• Find it fast. A sale comes in and the code tells you the shelf or bin. No searching through bags.
• Pack the right item. Similar items look alike. A code on the tag removes mix-ups.
• Avoid selling it twice. If you list one item on eBay and Poshmark, one sheet shows it sold so you can end the other listing.
• Handle returns. A returned item goes back to its slot and its record reopens.
• Know what you paid. Each code carries its cost, so each sale shows its margin.
• Cleaner records. Purchases, fees, shipping and sales line up for your bookkeeping and for a CPA. See Form 1099-K.

Shipping labels: one tool worth knowing about

Once a sale comes in, the label is the next step. Many small sellers use Pirate Ship, a web-based shipping tool for USPS and UPS labels. Here is what the company says about it, and why that helps a fulfillment routine:

• Free to use. Pirate Ship says there are no monthly fees, payment fees or hidden costs, no credit card is needed to sign up, and that it is paid by the carriers, not by you.
• Lower rates. It offers USPS Commercial pricing and UPS Ground discounts, plus access to Priority Mail Cubic. It advertises savings of up to 89% against retail rates. Savings depend on package size, weight and destination, and UPS discounts may change.
• Choose a carrier and speed. You can compare services side by side and pick the cheapest or the fastest for each package.
• Easy for a routine. It runs in a web browser. You can save presets for packages you ship often, print many labels at once, import orders from a spreadsheet, and track packages and keep receipts in one place.
• Help when you need it. The company lists email and live chat support.

Limits and downsides

• Two carriers only. Pirate Ship offers USPS and UPS. If a buyer or a rule calls for another carrier, you need another tool.
• Size and weight limits. Its help pages list a 70 lb maximum for USPS and 150 lb for UPS on domestic services (UPS Ground Saver is 70 lb). Heavy or oversized items may only show UPS rates.
• Some options are missing. Its help pages say UPS return labels are not supported, UPS is not available for hazardous materials, and some addresses, such as PO Boxes or rural addresses, may not show every carrier.
• Insurance and claims. Check the insurance terms before you ship anything valuable. One user review on Capterra describes a lost international package where only the label was refunded. Other reviews describe smoother claims, so experiences vary.
• Support and integrations. Because it is free, some users say support is less extensive than paid tools. Some sellers also want direct connections to more marketplaces and sales platforms.
• Savings vary. The best rates apply to some package types and weights. Light, small packages may cost about the same elsewhere, so compare for what you actually ship.

Marketplaces have their own shipping

Most marketplaces now build shipping into the sale, so you may not need an outside tool for every order:

• Poshmark sends the buyer a flat-rate prepaid label, commonly reported at $6.49 for up to 5 lb. The label is created for you after a sale.
• Depop provides labels at flat-rate tiers based on weight, charged to the buyer at checkout, as reported by a reseller guide.
• Mercari offers a prepaid label program with weight-based rates, and the seller or buyer pays depending on the listing.
• eBay lets you buy discounted labels inside the platform. You choose the shipping method and who pays.

The upside of built-in labels is convenience: the address and tracking are linked to the sale automatically, and some include tracking or protection programs. The downside is that you give up some control over the carrier and price. Whether you may use your own label differs by marketplace and by sale type, so check each platform’s current shipping policy before you buy a label elsewhere. Many sellers use built-in labels where they are required or convenient and a tool like Pirate Ship for direct sales and platforms that allow it.

Pair it with your SKU system: put the SKU on the pick list, pack the item, then print the label from a saved preset. That keeps shipping costs in one record, which makes your books cleaner too.

Flipfiled has no affiliation with Pirate Ship and receives nothing for mentioning it.

A format that works

Keep it short and readable. One common pattern is category code, month bought, running number:

• JW-2610-014 is jewelry, bought October 2026, the 14th item.
• SH-2611-003 is shoes, bought November 2026, the 3rd item.

Give each category a two-letter code and number items in the order you buy them. Do not put prices or private details in the code. If you buy a lot of identical items, one SKU can cover the lot, with a quantity column.

Set it up in five steps

1. Make a spreadsheet with columns: SKU, item, date bought, where bought, cost, shelf or bin, platform, list date, list price, sold date, sold price, platform fees, shipping cost, status.
2. Label each item when it comes home. A tag, a sticker or a bag label.
3. Label the shelf or bin and record it in the sheet, so the code leads to a place.
4. Put the SKU in the listing. eBay has a Custom label (SKU) field. Check whether Poshmark and Depop have a field, or use the private notes or the first line of your own sheet. Name your photo files with the SKU too.
5. Update the status when it sells, ships or comes back. Do it the same day.

Keep purchase paperwork together

File the receipt or a photo of it under the SKU or lot number. If you buy inventory for resale from a supplier, keep your CRT-61 information with the purchase record. Ask a CPA how to track cost of goods in your situation.

Start small

You do not need software. A spreadsheet and a label maker are enough for the first few hundred items. Move to inventory software only when the sheet gets slow.

This is a practical guide about organizing your inventory, not tax or legal advice.

I am not a CPA or an attorney

This page is general information, not legal or tax advice. Rules, fees and forms change, so confirm with the agency or platform. For advice about your situation, talk to a CPA or an attorney.

Sources: Pirate Ship (company website, claims are the company’s own); Pirate Ship help: why a carrier is not available; Capterra user reviews of Pirate Ship; List Perfectly: marketplace shipping fees (secondary source). Checked Oct 27, 2026.