Here’s a what I do in my industry: Architecture. I refuse invitation to tender for services where there are more than 3 bidders. I phone the person managing the tender and ask if they have a preferred Architect already and I say that I don’t mind if they do and I’m happy to provide a tender so they can show they’ve tried to get 3 bids but I would rather not waste a week putting together a proposal and a concept design etc. This works well for me.

Open tenders are typically won by firms that specialise in scatter gun bidding and the results will usually be poor quality. A firm with a good design track record doesn’t need to win work this way so they won’t waste time on them.