I'm dealing with another common version of this right now. Another contractor (not from my company) had estimated a certain amount of time to fix everything and

I'm dealing with another common version of this right now. Another contractor (not from my company) had estimated a certain amount of time to fix everything and add some updates to code they had developed. Our mutual client didn't want to renew with them so asked if we could do it. But lo and behold, the deadline was two days from now so the sooner the better. I cut down the estimate by half but said it wouldn't include fixing anything since presumably they were living with existing bugs in production they could keep living with them if the new features were the priority. I did say that we would have to pay the piper eventually and that this rushed timeline would mean we would miss things and that it was only possible if we had everything in place to do the development work. Things like access, correct data, properly setup environment etc. Of course we started development and had none of those things. I did get it out on time according to my shortened estimated. But then they discover that they absolutely do need some fixes and that the assumptions the dev team had to make because we didn't have real data were wrong so the whole thing is delayed by about as much time as the original estimate but there's a whole bunch of hand-wringing and people thrashing about because of "slipped timelines". And I knew this going into it. No one ever hears "But we will have problems I just don't know what they will be" They just hear "I can get it to you in 3 weeks"