The best possible advice I can give for making money on eBay is to sell with integrity.
Be sure to have precise measurements on your listings, so people know exactly what they are getting. There is nothing worse than ordering something from a picture, only to get it and find out it's way smaller or way larger than it looked in that picture.
If there are any flaws, no matter how small they are, be sure to make a note of these in your listing, and if possible, have a close up picture pointing out the flaw(s).
Put in more than one picture, and try to get different shots of your item - close ups, a different angle, front, back, sides - the more pictures to really get a sense of what the item looks like the better in my opinion.
Make sure you leave feedback for your buyers. You won't always receive feedback from your buyers, but be persistent in giving it. When I'm buying on eBay, I always check to see what kind of feedback that seller leaves for buyers as well as what kind of feedback they receive as a seller. Good feedback will speak volumes to people looking at bidding on your item.
I've sold successfully on eBay for many years now. Everything from used items to items I have constructed myself, and also my graphic services. I'm proud to say that I have a 100% positive feedback rating of over 800. And with that, I figure I must be doing something right.