It seems almost too good to be true that a $500 machine can completely eliminate the smell throughout a 2,000+ sq ft house. 

Hi @Adam Stroik you have every right to charge them that way, and it is definitely not unethical as you are the one who will be paying to repair and maintain the machines.

Coin machines?

Any other pet add-on advice is appreciated.They are smoking on the patio, also expressly against the lease terms.They are into organic gardening, which is fine, but has resulting in a bit of a swarm of fruit flies in the dining area.

One of the reasons payment wasn't "received" was that the check was lost in the washing machine. 

what about the more heavy duty white noise machines?

You got to start from the seed, to get to the root, to get to the fruit.

I do not send letters because I do exactly what Rick said and do my title due diligence before reaching out and look for the best deals and the low hanging fruit, then I skip those people using my own techniques which I posted in another post. https://www.biggerpockets.com/forums/93/topics/290841-ugly-abandoned-house---where-can-i-find-the-owner I call these people personally as these deals are golden and get probably a 50-70% closing rate by solving problems.I hope this helps.

The deal looks like this.5 Bedrooms/ 2 full baths large yard with 7 fruit trees security system on windows New Rooffull fence Two car garageShe had it listed for $170,000 but the Agent claims that she didn't have it on the market for long enough. 

My house is built in 1925 with thick beautiful hardwood floors all through out, I was looking to hire a professional but it is so expensive when I can rent the machine for about 50$ a day.