I think it is a big mistake if you don't charge a deposit equal the cost of the meter. By taking the deposit, people will treat the meter far better knowing that if they damage it, they bought it, rather than if they are just charged a small fee and know that if they damage the meter they aren't on the hook for replacing it. I put several hundred dollars on my card every time I rent a tool (which I have done about half a dozen times), but it doesn't even worry me because I take care of them, use them the way the are intended, and return them without a problem. Same thing would go for the meter. 

 

I also think that you need to write up some sort of rental agreement stating the conditions of the deposit, rental, etc...that is signed by the renter at the time of rental. All of this is just to protect the owner of the meter.

 

If these things that I mentioned aren't done, I think the owner is just asking to get burned.