Either handled and or managed procurement for major corporations all my working career. First you should make sure all bidders are of equal status as to capability. You work for your company and your responsibility is to get the best overall offer. I often would give suppliers general information as to bid status. To ensure my company got the best deal. If a company who had a proven performance and may have been previous supplier with excellent result. I might say you are too high. Sometimes I would do so even if they weren't to make sure they didn't have extra cushion. No one has to take a job.

I dealt in this field for over 40 years and maintained total ethics never took a dime but I was occasionally offered bribes. I can always look myself in the mirror and know my company's interest was always my priority.

Yup....lowest bid usually bites you in the butt....

Yep I’ve been bit several times but my hands are tied 90% of the time. Government forces me to take the lowest bid and if I don’t I better have some rock solid documentation as to why I went with a higher bid.

You may not want the lowest bid.
There's usually a reason that it's the lowest.

Old rule of thumb was - three bids -
Throw out the lowest and the highest.

Probably a good rule to follow....

I have found this paradigm to be consistently true:

Absolutely not.

Man up and just buy from the best salesman.

It's not an ethical practice, but happens none-the-less. Over the course of my career in the construction industry I have become pretty good at identifying companies wanting bids from me so they can use my numbers to beat up their preferred contractors and get better pricing. I quickly stop dealing with companies who practice that.

On the other hand, many times projects must be competitively bid out when one contractor already has the project locked down, and I am often "that" contractor. We provide turnkey service from design to handover of the project, so other contractors are pretty much screwed to begin with, and most will often take the bait in hopes they can unseat us, but they are hardly ever successful at doing so.

The methods used to award projects have changed a lot in my industry over the last few decades. Contractor loyalty is almost a thing of the past, instead companies will award to the lowest bidder regardless of how well they have covered the project requirements, then literally be more than willing to bankrupt a contractor's company in the process of getting the bottom line they had on paper in the beginning. In the end those projects often end up over budget, and over schedule, when it would have been more efficient to just pick a reputable contractor who had their bases covered in the original bid. You'd think the customers would learn lessons from those instances, but most seem to continue down that path anyway. It is truly puzzling sometimes.