USA Tax and Reciepts/Proof

[BusinessMan10123]

Okay keeping it simple. I basically purchase things from garage sales and local people and post the items online for sale on eBay/amazon. Problem is that I have no way to show my actual cost of goods sold on paper. What I have done is create a paper receipt of the date and item and price I paid, no name of course from the person buying it as I do not know who they are. Is this acceptable? Is there a better alternative? Any help is greatly appreciated. Thank you.