I don’t understand the desire to tell totally anonymous third parties the terms under which they are allowed to deal with each other.
Many kinds of contracts are illegal, including those that are anticompetitive in certain ways.
> Should I be allowed to pay a landscaper less if I agree to not do part of the work myself?
No?
Right, so they're not voluntary.
1. There is one supplier, so you have no choice. 2. Even if you had a choice to sign the contract, this still means that it's not the same as a trade-in, because trade-ins are always voluntary, but once you have signed the contract, a right of first refusal is not.
In general, the "you chose to sign the contract" argument is a poor justification for bad contracts. If the contract is bad, it is bad regardless of whether you chose to sign it.
As businesses are expected to be more informed and equal in the negotiations