Perhaps I'm being paranoiac, but are you sure you are not getting scammed? Why do they need a reseller? Did you know the big client before getting fired? Did you know the software before getting fired?

Resellers are not accountable for these items. The contract is between the SaaS and buyer, you have a contract with the SaaS company.

You can search for MSA agreements on RocketLawyer and find language you can use in your own agreement.

A plain language agreement can work.

People only sue people who can pay. You obviously can’t.