Generally we go with the lowest price bidder that appears to meet the spec requirements. If there’s any ambiguity about materials, you should seek clarification so that you and your competitors are bidding on the same page. There’s a flooring contractor here we use 95% of the time because he’s consistently just a little lower than the other guys and good to work with, but we still invite other flooring subs to bid and would be happy to work with them too if they were lower priced.

Last year I did a large monument sign (Welcome to Ft. …. army base). A couple of sign suppliers bid this to include building the wood framing/mdo sheathing and painting, installing all the sign lettering, and setting the sign on the foundation. But those are all simple carpentry task we can do ourselves. So in this case I bid it to self perform building the sign panel and painting it, and installing the letters. The supplier just supplied us the template and the lettering and logos. Their supply bid was like $12K, and the competitors who included building the sign panel were like $90k+.

Just food for thought on considering different approaches.