That’s the thing with profile. ;-)
But you can create a test Tiki to see how it work and apply in real life (that’s how I usually do).
While we setup a very advanced shop using Tiki 12 I can’t tell you a lot about older version.
I use only fresh versions from the oven and have no clue if and how it work today on 18.
But you mentioned you need a small market place. (nothing is really small about selling things and you need control and transparency).
I would use a tracker (user can create) to store the items (text, images=>files) and calculation (VAT, shipping) and a plugin list with a Paypal button.
Paypal will do the invoicing.