Tenants in this class are more likely to have pets even though you so no pets.

Is it unfair to ask for no pets in the other unit? 

Other things we would like to consider are pet type and size (we accept pets), references, income etc.. 

I have security cameras (mostly so I can prove if a guest violates the no-pets rule or throws a party, etc) and wifi door locks.  

She stated that should had no problem paying pet rent for her non-ESA dog, but not for her ESA dog.

Is there any difference in the frequency or extent of the problem with the number of people and/or pets in the units?

Some States it may be illegal to charge for water, so increase it for another matter.If you have a no pet policy, make sure they know it.

Part of our lease says No Pets.

That way the tenant knows all the ins and outs from quiet hours, bbq restrictions, parking, pets, and more...But check with a professional or your NY rules if you have specific questions about your situation.Best of luck!

I think pms are moving towards requiring tenants to provide receipts that a professional cleaning was done, carpet cleaning if carpet and flea spray if pets.