I read this program allows classified listings, but does it allow people to upload photos, information and pricing- which will post immediately to the website for sale? Also, once someone clicks "buy" how does it make sure that the visitor gets their money and the web owner gets their cut? I'm looking at starting a website similar to Poshmark or Threadflip. I have built many websites and am very computer saavy despite not being in the IT business, but don't want to hassle with difficult programs. 

Yes, the UltimateWB Full version has a built-in Classifieds app.  It does allow users to upload photos, information, and pricing.  You can customize how you want listings to activate - such as automatically after they submit it.

You can also charge for posting ad listings and/or for adding special features to it (such as photos, highlight, feature, etc.), and have the ad listings activate automatically after you receive the pament (via PayPal).

You can configure the classifieds to allow users to use a "buy" button.  User purchases can be made via PayPal accounts, or alternatively using your website Credits system, where users buy credits on your website to then make purchases with.  If you would like to charge a percentage of the user transactions, you can do this automatically on your website by choosing the Credits system as the User to User Payment Processing method.

All these settings can be configured on your website admin panel, Configure Site > Social Networking > Classifieds section.

You can get a good feel on whether this software is a right fit for you by reviewing the online Resources available:

User Manual: https://www.ultimatewb.com/user-manual-how-to-guide

Quick How-To Guide: https://www.ultimatewb.com/quick-how-to-guide

Video Tutorials: https://www.ultimatewb.com/video-tutorials

and the online Demo at: https://www.ultimatewb.com/demolinks

Please feel free to post if you have any further questions.