I'm a buyer.
Forget compelling as such.
Think accurate, factual, detailed, set out so it can easily be read.
I quite like bullet points for some items.
You need compelling photos-clear and several of them.
You need measurements or sizes.
If your item is like several other items on ebay, then you need the point of difference-quality? brand?
You can set out sales terms in the ad but if they end up longer than the ad itself, it is a turn off. You really don't need to add much.
Mainly (as far as I am concerned) your ad has to come across as clear and detailed enough so I don't feel I have to ask you several questions, but that you probably would be helpful if buyers do need to see extra photos etc
Maybe have a look at other ads in the sort of categories you might sell in. See which ones appeal to you the most and try to analyse why.
