think about the size of the parts........if selling fenders, you might want to have pickup at your home. If small pieces, then shipping is fine. Flat rate boxes work well.
Ive taken personal checks, but if youre worried, get a money order or bank check sent to you.
Different venues sell parts and cars at different rates. the barn is fine for selling, but sometimes will be very slow. I prefer Craigslist for local pickup..... or ebay.