Well donations are anything that you give that has some form of value, even if it's pennies it's still technically considered a donation. And with donations there is no set limit, it's more of give whatever you can(or want)
once you set a minimal price that you will except for your merchandise you just converted the transaction into a sale.
sale *(sl)
n.
1. The exchange of goods or services for an amount of money or its equivalent; the act of selling.
2. An instance of selling.
3. An opportunity for selling or being sold; demand.
4. Availability for purchase: a store where pets are for sale.
5. A selling of property to the highest bidder; an auction.
6. A special disposal of goods at lowered prices: coats on sale this week.
7. sales
a. Activities involved in selling goods or services.
b. Gross receipts.
[Middle English, from Old English sala, from Old Norse.]