I'd just recommend to use a software for shopping purposes, not a forum. They are different things.
For the forum itself, miniBB has nothing to recommend. It has a strict structure of database, which preferably should not be changed.
But you have all rights and possibilities to change it, it's under GPL and it's open source. It's up to you. Change the database, assign all fields in all other related scripts, add-ons... share couple of months for coding/testing... came up with another ideas... up to you.
We do not provide recommendations or advices regarding such requests, even in paid service terms.
Because it's usefulness job.
Fair enough. I have calmed down now on this idea. This is me all over. Some idea that enters my head and I will rush forward without really thinking. All I had to do was create a new forum for 'Expired Offers' and move the offers over to that forum when needed.
As for using the forum as a shopping site? It is still being used as a forum but is the front end only, with the shops in subcategories on the same domain.
I think my forum looks pretty good now. Don't know what you think?