I've been selling on Ebay since the Beanie Babies fad and I have had my run-in with quite a few Ebay buyers. Here are a few things to remember so that you don't join my Buyer Block list or be the topic of discussion on an Ebay seller forum.
1. If it's too good to be true then it is too good to be true. If you pay $15 for a box of rings and expect them to be from Tiffany's, you shouldn't be shopping on Ebay or the internet in general. Look for Ebayer sellers with lots of great feedback and stay away from sellers with lots of negative feedback. Just like you discovered with your ex, you are not going to be the one to change them.
2. Don't be an annoying buyer. Having a question or two is fine, but having a lot of questions sends up a red flag to a seller. I currently have a buyer who contacted me after the purchase and stated he "just HAD to have" the item I was selling. Now I get an email every 3 hours or so with a different question or comment: when are you going to ship it?, when is it scheduled to arrive?, sorry, I meant to send the last message to a different person, where do you check the tracking?, etc.,etc. Unfortunately I didn't realize I had sold to a crazed person until after they paid. I protected myself by marking my item with a seller's mark, taking a picture of the item next to the printed shipping label, and having all communication with the buyer go through Ebay Messages only.
3. If you have a hard time finding things in a brick and mortar store that fit you the way you want, or are just the perfect color that you want, or you like things you buy to be in your hands yesterday - then don't buy on Ebay or again, on the internet in general. There's a very good chance you will probably be just as unhappy shopping online too. One of the funniest questions I got from a potential buyer is "It says it's a size 8. Will it fit me?" Keep in mind, #1) I ALWAYS put measurements in my listings and #2) I don't know you! My other favorite question is "how soft is this?" Whaaattt? How does one measure softness?
4. READ THE LISTING DESCRIPTION <---- 'nuf said.