Ill fo first. My favourite products are something that people can have fun with. I have noticed that when people have fun with renting you product than most likely they come back and rent it again.
Example: Surfboard and sup boards, bicycles and electrical scooters and soo on.
And always give visit card with contacts soo the person have the email and on the card there can be a code for discount. Everyone loves discounts. And it dosnt need to be 20% or more. 10% is enough. Soo now he has 2 reasons to rent the product from you.