Some years ago I found a niche and started selling slot machine reference guides, historical books, and repair manuals. I did pretty well. Not much of a margin as I was using Andale AND PayPal (before eBay kept track of the sales).

I met a few idiots who didn't believe in paying, and some who didn't like to pay postage on a book. But that hasn't been the norm. In fact, in over 3000 transactions, both as a buyer and a seller, I've only left or received 6 negative feedbacks.

Needless to say IMO anytime I left a negative feedback it was richly earned, and each one I've received wasn't.

I've learned:

1. Be Customer Focused
2. Always use Delivery Confirmation
3. PayPal is the ONLY form of payment accepted
4. Require payment within 5 days
5. Send a reminder in 3 days
6. Don't buy or allow buyers from France