Best way to lock in a future deal?

[Tom Rittenburg]

I am working on a deal to purchase a seasonal short term rental property next year. We are 99% there as far as negotiations, and fortunately both the seller and I are on the same page that we want the transaction to happen at the beginning of next year's rental season. The seller wants rest of the income from this season, and I don't want to hold the property over the winter.

The big question to the community - what is the best way to lock down the deal. I want to make sure the deal is sealed and that the seller won't have an out. I don't know that a boiler plate P&S is strong enough to prevent the seller bailing and going with a more lucrative offer at some point over the next 8-9 months if one should come along. Is a P&S with a large bailout penalty out of the norm, or unenforceable? Any other ideas, or ways that people have done this?

Thanks in advance!