If I accept a bidders pricing, does that award them the work?

No. Accepting a bidders pricing simply adds that pricing to your billing item library. You will still need to make that vendor selection on your Work Order and submit a Purchase Order to the vendor to award the work. 

To help clarify this with the bidder, they also get an email, after they submit their pricing, letting them know that the builder will generate a purchase order, if they're selected for the work.