Can I Patent a product or method of using said product that’s been for sale 3 years by myself the inventor.
Is this possible or not?
If not, what, if any protection does inventor or said company selling said product have?
It is not.
Patent should be new, and new means never published.
If you used it for one year than in the united states (other countries wouldn’t accept it) you could have agrace period,
but after so much time it is public domain.
But it is always advised to consult specificaly, maybe you have a goodwill that could be expressed by a trade mark, maybe you cuold improve your invention and patent the improvment itself.