When I look at things on Ebay, the first thing I do is subtract the shipping amount from the price of the item at my local hobby shop. The result is the price I am willing to pay for anything on ebay. Lets say an Athearn boxcar goes for $5 at the hobby shop, and the Ebay seller wants $3 shipping...I am only willing to pay $2 for the car. If it has been put together, it is worth even less to me; they have taken the fun out of it. The item has to be REALLY special for me to do otherwise.
I tried selling custom stuff on ebay once. I made a couple bucks but not enough to get excited about. My local hobby shop once got rid of all his Athearn locos by selling them for about 1/3 of his normal price. I bought a half dozen or so with the intention of selling them on Ebay. I tried selling them (stock paint jobs) for $20, only to find that there were hobby shops on ebay, dumping the same models for $8. Cant compete with that.
I repainted them, and sold half of them. I still have the rest. The ones I sold paid for the ones I have, but just barely.
To sell a standard, stock Athearn loco is one thing; but the minute you do anything to change it, you accept responsibility. If the buyer doesnt like what you did, you eat it. I kitbashed some cabooses and tried selling them...I sold one. The guy promised to buy a bunch of locos from me, but I never heard from him after he bought the one caboose . Dont know if he was displeased, or what. Its a different story to sell things at a flea market or through your local shop...the customer can see what he is getting before he buys. But ebay is different...they cant see before they buy. With the time it takes to make the images, edit them, and make up the ad, plus worrying about whether or not the customer was going to like it, Ebay just wasnt worth the trouble. (Now my sister is a different story, she can buy coffee mugs at yard sales for a quarter and sell them for $50. Dont know how, but she does it.) YMMV, Bill