I honor my estimates to the scheduled date. If they need to reschedule for weather etc, still valid as I agree to do the work. If the reschedule is my doing (my fault) I will honor the price at the new scheduled date.
If they cancel the job, it nullifies my estimate. Basically, that is the thirty day thing. Canceled indefinitely best call back in 30.
I did one, I don't know, about 8 years ago. Quoted 750.00 for a pretty simple oak TD. Really only needed to be partially roped down and then felled. stage brush for burn, leave the wood. They told me, not at this time.
8 years later, call me and ask if I would honor the bid. I told them no. I would have to look at the job again. I know these folks. They have cluttered the work zone and the tree is in further decay.
They call a competitor and ask for a quote. He quotes about 1200.00..
They try to leverage him with my 8 year old bid.

He calls me... WTF are you thinking dude? You under cutting everyone? No way for that price!
I enlighten him about the age of the bid. The whole scenario of then vs now. Told him I have other clients on that road and have driven by every so often. Tree is in shit shape, has new hollows and fruiting bodies, dead tops. Home owners have added more stuff in the yard as targets. Gave him the whole bunch of beans. Also told him that they will never get me to set my foot on their property again for work since they tried to leverage his price with my 8 year old one. Seriously. You game shit like that, you don't deserve to be my client.