I’m not knowledgeable about odometers at all, but if it’s as easy as “hooking up to a computer” to get the real mileage, why don’t people do that when they buy the trucks?
That said - odometer fraud is a big fucking deal here. A vehicle with unknown mileage is worth far less at auction (just the fact that it's unknown is a huge flag) and if the auctioneer was aware of the fraud (as they're implying Holman Fleet Leasing was) then I'm curious to see how this is resolved... a smaller auction house would likely see jail time for several employees.
<https://en.wikipedia.org/wiki/The_Market_for_Lemons>
Moreover, many states require regular smog checks, at least on passenger vehicles (though I'm not sure what the situation is for commercial vehicles). These entail a comprehensive electronic data record, much of which is automatically captured from the vehicle, and which is available for sale. Auto insurance companies have used these data for years, if not decades, to set policy rates as miles driven is a principle driver (ahem) of risk.
If VINs are avaiable for the vehicles being auctioned, it's possible that a service such as CARFAX might carry such data. I suspect bulk / corporate buyers would tend to have access to such information, whilst small-time operators / individuals likely would not, which throws an additional bias into such auctions.