But they said they still have fleas.At this point, I feel like it is fairly safe to say that they brought the fleas in with them or at least their cleaning habits (or lack thereof) have contributed to the problem.Anyway, my question is who is ultimately responsible in this case? 

I am building capitol to flip myself and think it makes more sense to make sure you can have as clean an inspection as possible.

They are now clean, according to their Instagram, or Twitter, or whatever.What goes through your mind, and how does it play into your overall evaluation?

For the second property, I created a checklist and told him that he will no get paid until all items on the checklist can be checked off and the quality of work is acceptable.

***DISCLAIMER*** I Own & operate a cleaning business.

The quality of inquiries was much better there than craigslist as Zillow inquiries can come with tenant info (income, history, credit range, pets, smoker, etc).

They are not good at quality control and hence the inspection process itself, and the resulting paperwork, is done really poorly. 

We did one..we bought the home next door & initially we got $820/mo in a 70's era SFH in very very tired shape.When they moved after 5 years we rehabbed it for $18k & got $1400/mo & that was 6 years ago.We did bump the rents over 2 more tenants (now $1650/mo) but the current tenants do all the maintenance.When the 20 yr old HW tank burst at the seams they shut everything of, cleaned up the mess.

Alright so for actual advice I would find a tenant who can maybe do handyman work or keep the grounds clean, etc for reduced or likely free rent.  

In the meantime fix the rental up and rent it to good quality tenants.