If you can troubleshoot all the problems from toilet flappers, to clear drains, and all moving parts cleaned and working well BEFORE the tenant moves in, it will reduce calls.

He also didn't even tape it properly (still gaps), didn't press it down all the way (my friend did), and left pieces of insulation all over the floor.Handyman checked pipes under the kitchen sink to troubleshoot why dishwasher drainage floods the kitchen.  

I ask where they've seen the bed bugs so I can come and inspect and they claim that such a question is proof that I knew of the bed bugs...After going around the world with this guy to explain that this is a normal troubleshooting step, identify where they've seen them so I can come and look, he claims he only responded with logic and that I'm wrong....Then he sends me another email telling me I'm being volatile and defensive...Then this beacon of logic asks me at 10:00 PM what time in the morning the exterminator will be by.

It depends, if she is good, keeps the place clean and pays on time and hasn't been much troubleshoot.

For me I can troubleshoot furnace issues but if I have a tech come in and tell me the repair will cost a couple hundred bucks I'm replacing an older furnace o a more efficient model every time. 

We had to replace an entire additions framing as a result.When troubleshooting a backed up sewer line we discovered the original owners had tied their lines into their neighbors.

Hemlane provides an actual service (assuming "Smart" plan is used) where they receive the request, work with the tenant to figure out what's going on and try some basic troubleshooting and then if needed call in the professionals and make sure everything is done to the tenant/owners satisfaction (pictures, invoices, etc.).

Quote from @Jonah Stavsky: Pay the bill and consider it your tuition fee.You should always try to troubleshoot problems with the Tenant before sending an expensive technician.

You can try to troubleshoot with the installer and get them to make it right, however if they are unable or unwilling, you could have to look into getting a refund on their work and finding another installer to put in the windows.

@David Eiges I can't help you trouble shoot.