The only thing to keep aware of is to not abuse their time (sounds like that won't be an issue).

It’s not right to hand over so much power to tenants who abuse the system.

@Daniel DietzWhile the cases cited are analyzing a different context (estate and gift taxes vs in-plan Roth conversions), in 2004 the IRS identified "Roth IRA stuffing" as an abusive tax avoidance transaction which has parallels to this concept in that the assets are being shifted to a Roth account below fair market value. 

They deliberately abusing landlords' compassion and taking advantage of their kindness.Today I finally met these owners which I tried to get in contact with for a while, because of continuous disturbance from their tenants. 

I don't think adding another element to the arrangement that could potentially cause disputes is smart and I haven't had anyone abuse the heat/AC over the several years I've done this so I plan to keep it that way. 

They never walked the dogs which i think is abusive.

This is where you show that you won't just sit back and take abuse and that you have a backbone. 

Since I've lived here I have a pretty good idea what the bill is like, but I worry about tenants abusing the utilities. 

Quite the contrary, it has been rejected at many companies due to employee abuse and the inefficiency it creates.

But I’m just not comfortable paying the utilities, as they rent is not high enough to justify the expand potential for abuses.