is it illegal for me to demand my boat slip rental customers purchase supplies from me only?

Yes.

Yes it is illegal and so are the other contracts you posted because you can't draw up these contracts to fine people for anything. It is not a legal business to invent fines/ write business law contracts without a license to practice law. After if you are a lawyer, you would be disbarred and changed with racketeering, you have no license from any Govt agency, that allows you to do these practices. Simply, there are consumer rights laws, banking laws, usury laws, secured transactions laws, credit laws that protect consumers etc. and you would surely have violated everyone of them. Because of that, you could not enforce the contract or collect one cent of the fines. You also stand a risk of being arrested for as a con artist, bunko: Informal. swindle or scheme that takes advantage of another's ignorance. A swindle in which an unsuspecting person is cheated.

Sorry, that's not legal nor ethical.

You have no ownership over the boat and have no legal rights over the boat, only over the marina space.

you're fantastic as long as that that's made sparkling interior the apartment settlement or by utilising technique of a few form of notification on the time of area apartment. in case you do not have a apartment settlement that states this and criminal accountability counsel you had extra advantageous get one. you depart your self extensive open to all kinds of issues.

Yes.

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Can't do that..