Three bids is standard corporate protocol.
This is a new one on me.
Guess the corporations I've dealt with play by a different rule book.
More or less?
Three bids is what I experienced with a Fortune 500 company and with the federal government.
One bid doesn't give you any comparison if they're charging you twice the market rate or offering such a low price that they will potentially cut corners or ask for more money later.
Two bids gives you some comparison but you could end up with two people both bidding high. Of if you have one bid much higher you don't know if that's the one trying to overcharge you or if the low bid is the one who doesn't know what they're doing.
Three bids means you can either determine that all three are about the same or eliminate the one much higher outlier, or if it's a lower outlier see if they are really accounting for the same scope of work or will provide the same quality of work. It potentially gives you some negotiating power as well.
Beyond three and it's starting to add more time to vet those bids, plus you may not have that many vendors who will supply bids. I know that varies by product/market. In a big city you could probably find a dozen plumbers who specialize in sewer repair. In a small town there might only be a handful of plumbers and maybe just one or two that specialize in sewer repair. The bids from them will be more valuable than the plumber who normally just deals with water heater replacements and unclogging toilets. That's the one that might bid too low because they're not familiar enough with the work to know how much it will really cost. They might end up making no money and do a good job. Or they might cut corners to still eke out some profit and you could end up having to pay someone to redo it down the line.