Low Bid the Best Bid?

Of course not! The low bid is simply that: a price submitted to gain the work being offered and it may not even reflect the vendor’s best product, just the product that may meet the minimum requirement of the project.
Important to consider is that the product/services submitted are generally the one that produces the greatest profit margin for the bidder. The client has to be sure that the product offered will meet or exceed the requirements of the project, not just the minimums. When involving ongoing services such as elevator maintenance contracts which are normally but not exclusively; a 5 years deal, it is important to look at the overall value of the bidder’s service history and local strength.
A bidder that submits a higher monthly cost may be doing that realistically to meet the contracts objectives and still entertain a reasonable profit for its owners. Nothing wrong with that. We desire the vendors to be profitable; that’s just good business. What is wrong is to submit a price that is known to be unrealistic to meet the contracts specifications and then attempt to “bill your way to profitability” or to not perform as required by the contract.
In a typical construction or modernization project, a 5 year maintenance contract may be a part of the bid package with the maintenance portion to be consecutive with the end of the warranty period. That maintenance price would have been itemized in the original bid so its price can be examined to determine that value to the client in the long term picture. Part of bidding process to chose a vendor includes the comparative of long term service relationship and initial construction costs to best select the winning bidder.
Suspect would be abnormally low construction cost far below that of the next few bidders. Elevator company to company comparisons show that materials and labor cost somewhat even the playing field. While union labor can substantially increase that cost for those vendors, efficient installation procedures with products developed to reduce the labor expended often offset the higher labor cost. Nonunion labor vendors may have the edge in labor cost but are likely to be non-manufactures of the equipment and will pay a greater amount for materials. Of course there are exceptions to both scenarios.
Abnormally high bids may indicate a poorly drafted bid specification or other factors that caused the bidder to protect themselves. It could be that their labor costs are significantly higher in that area or their product may have to be modified to fit the project.
Bids have to be clear and free of any ambiguous language. It’s to the clients benefit that the bid specifications are drafted to contain exactly what is required. That way the true costs are known and the vendor has the expectation of a reasonable profit in exchange for its services.
Separating the chaff from the wheat is the work of a knowledgably consultant.