In my experience, bids for a well defined scope of work will generally be plus or minus 20%, so within a 40% range. There is a reason for this...there is a certain cost of doing business and there is a certain amount of time and resources that must go into doing a job. In order to bring the price below a certain level something has to be compromised.
Let's take a lawn that on average would go for $50, based on my 20%. That would mean one contractor might bid it at $40 and another at $60. That's a normal range. It wouldn't be fair for the $60 guy to be calling the $40 guy a lowballer. However, if someone were to bid it at $25 or $30, that would be lowballing in my opinion, and logic tells me that they're going to have to cut corners somewhere in order to provide the service at that price, and that their long-term ability to continute to provide the service at that price is questionable. It's not uncommon for some companies to deliberately lowball jobs just to get them and then once they have the job to exceed their price, citing all sorts of reasons that they claim could not be forseen...not something that's easily done for mowing services though...the scope of lawn mowing is pretty easy to define.