You can download a list from Paypal. Ebay only goes back 90 days but you can automate downloaded reports from there to get them monthly.

I use the Specific Identification method to value my inventory which means each item is assigned a unigue cost. After I make a purchase, I enter the item in a spreadsheet along with what I paid for it. I then copy each item into a base listing in TurboLister (which I will update later with pictures, description etc) with the cost of the item in the Custom Label field. Each month when I get my downloaded report from Ebay of my sales, I total what is in the Custom label field - this is my COGS for that month, which I manually enter into Outright. You could also use the Custom Label field to assign a SKU# which refers back to the item cost, but to me and the small volume I process annually putting the cost into Custom Label just saves me a few steps.

I also manually enter costs of supplies, mileage, and other expenses which are not captured by Outright. At the end of the year I pretty much have everything I need in Outright except for my home office expenses.

I'm a part time seller and cannot justify hiring an accountant, but I want to make sure I have covered all bases and am doing everything correctly. Unless you can afford to pay someone to do your accounting, you need to become very familiar with all the tax rules/rqmts for a sole proprietorship (or whatever type of business you maintain).