is it illegal if I demand my tenants to purchase home repair products from my store only?

It sounds pretty assanine if you ask me.

It may not be illegal but it is kind of dickish.

I have been a landlord and have had many rental properties.

You must be prepared for you tenant to call you every time they need a repair if you force them to only buy from you. They will just not do the repair and make you do it.

This will cost you more than any small profit you make on whatever repair they do.

You can not fine them for doing your repairs. They just won't do them at all they will let the sink leak till you have to replace the whole floor. I have seen it. Better for you to just deal with the repairs as they are needed. Small jobs are better and cheaper than big jobs.

Don't make your tenants afraid to call you if something is wrong in the house or apartment it will come back on you sevenfold.

You are responsible for repairs on your property not them. If they have to make repairs they are entitled to make them with materials bought where they please and bill you for the money they spent.

Aren't you the guy I sold the snake-skin oil to yesterday promising that it would "double your IQ or no money back" ?!?

This is a joke, right?

it is in the USA