I use a link to my website which has a form on it (only the form with no other products etc). However, If you need customers images it's a pain in the AR*E as when customers are using the eBay app it restricts JS not just on your listing but your webpage so any image upload buttons etc do not work.
So you have to tell your customer that if their using the APP the must go direct to their browser and load your web-page. I try to be as clear as possible in my listings but I still get messages most days from people telling me the form isn't working, I then have to message them back telling them to go to their browser and type the link. A lot of people don't know what this means.