Looking for a trade account theme, detail inside

So that the trade customers can upload their products themselves with images etc, Looking for a magento based theme compatible with 2.1.9 or 2.1.7

Yes, plenty of times.

Never seen multi-vendor hemes on here for Magento, also you may (depending on how exactly it functions) require an extended license)

There are multi-vendor plugins available so this may be your best option especially to give you the widest choice of themes