I'd also recommend that you make a strong promise that you're on the hook for any damage and that you'll pay the rent no matter what— plus possible some percentage of the upside. 

How much will it cost to repair damage from a water leak?

You will be responsible  for any code violations that he did, and if anything happens while he is working, damages something, gets hurt, you may be personally responsible and your homeowners insurance may not cover it because you are using an unlicensed contractor. 

A family member just had this develop where the neighbor's fence was damaged, and the neighbor told them, if you want a fence there, you pay to fix it, because I'm just removing it. 

It's also good for applying over damaged drywall. 

Here it would go to the new landlord to cover damages (along with whatever interest was made on holding it).So I see it as the new landlords (buyers) are given the funds to cover the damages the tenants (buyers) did to the property before end of lease.

Such as denied property damage claim from improper repairs, denied liability from not having the proper coverage, and workers comp penalties for paying people under the table to do work and them getting hurt.In this situation the agent who insures the primary home could have...1.

It's not optional.This is a good start: https://www.mass.gov/the-massachusetts-lead-lawIt literally takes a child ingesting a chip of lead paint the size of a quarter to cause actual brain damage. 

Said that if he can't get in that night, at least cover it so it can't get damaged.

If seller defaults, seller owes buyer $5000 in liquidated damages.