I've been in flea infestations and have a very bad reaction now when fleas show up.

The seller advised me of issues she had been having with the tenant including having more pets than allowed which resulted in a flea infestation of the entire building.

View, fairview you are seeing anywhere from 800 for a 2 bed ( a very run down roach infested 2 bed) to 1250 at the higher end for nice clean places.

DAY 1: We go looking at properties: we saw 3 properties.The first one had the signs (and smells) of a rodent infestation in the basement and the upper unit was in need of complete rehab.

Purposely infest the place (if possible ) with some fast breeding bugs, then watch them WANT to get out as fast as possible :) You could hire someone to do this for you maybe :) 

Just reaching out to all the more experienced landlords out there- One of my Detroit tenants has submitted a complaint of bed bug infestation in all her furniture.In your opinion,- is this the owners responsibility.

Tenant agrees to be responsible for maintaining a clean environment to discourage pest infestation and agrees to report to Landlord any signs of pest problems in a timely manner.

-Water pouring in because the Amish roofer who just put the new metal roof on is a terrible roofer-Having to knock holes in the wall so the plumber can repair the broken stack that's oozing you-know-what-Seeing my property on the morning news due stating one of my tenants was shot and killed-Having a massive tree smash a duplex-After evicting a tenant, cleaning food out of a maggot-infested freezer-Massive water bills due to running toilets-After move-out fixing all the things tenants damaged - time-consuming and not fun-Dealing with trespassers (happens a lot in C-class)That's what first comes to mind.

Now I have a opportunity to buy a house for 30k. the house would be worth at least 80k after makeover but the house has been highly infested with rats.

I wouldn't call it an infestation, but it's certainly enough to cause concern.