The architect should always act in your interest! If you feel that he does not, then take another one.
We did it, for example, like this:
Structural engineer (we have one in the family) created the drawings, tender documents, and building application documents for us.
Afterwards, we sent the tenders to various companies. The offers that came in (only about 30% actually participated) have to be checked and compared. Either you trust yourself to do this or you commission the architect/structural engineer again. After some craftsmen tried to cheat us, I would recommend having this checked by a professional as well.
When "all" offers were in, we took the two cheapest and had a personal meeting with them. In this meeting, we adjusted the specifications in detail and renegotiated the price including cash discount. The company that was the most likable to us and acceptable in price received the contract. Here we always chose a VOB contract with a flat rate to avoid any unexpected surprises.
The acceptance of the trades before payment was then again done by our structural engineer.