For general information and advice regarding listing / selling on eBay, you will likely find a wealth of knowledge right here on the forum, and for free. (Most people here are only too happy to provide some feedback on listings, and much of it will be constructive criticism, though often not sugar-coated 😉 ). 

We won't be able to do any manual work for you, obviously, but can provide lots of information for creating effective listings, including description, photo and title / keyword tips, so if you need any advice along those lines, please feel free to ask here and I'm sure there will be something useful and relevant in the replies. 

I'm assuming you want to maintain the listings yourself and on your own selling account, which would rule out an eBay trading assistant (TAs take your stok and sell it on your behalf for a commission), but the info given here can often help give you a more sound knowledge base from which to start.