Changing offer during due diligence period
I'm watching a video by Brandon Turner called How I Quickly Analyze a Rental Property for Cash Flow, and as he's filling out the BiggerPockets buy and hold calculator values (specifically, the repair costs), he says "we can always change these numbers later depending on what we find out [about the property]" (around 5:21 in the video, for reference).
Suppose the numbers appear to work out, so I submit an offer based on my first-pass estimates. I'd then go check out the property, make any adjustments to my offer, and resubmit if the seller counters. Suppose we then reach an agreement and accept an offer, then I discover unforeseen issues during the inspection.
I know I can back out of the deal (at the expense of my earnest money) if I added an inspection clause to the offer, but is it acceptable to stay in the deal and reduce my offer at that stage, even though we've already reached an agreement? Is that a common practice?