The creation and use of baluns was and is a band aid solution for the lazy. Coaxial cable exists for a reason as does Ethernet cabling.
Each one was designed for a purpose. The problem is man decided to repurpose these cables like they did for telephone:
DSL . . .
Than the cable companies pushed for deregulation so they could get a larger slice of the pie: TV, Phone, Internet
Than Ma Bell said FTS we need to make up for the losses and went from telephone to: Internet & TV
At this point you have tens of millions of homes with old ass wiring. The average person isn’t going to rip out existing wiring infrastructure and thus the media converter market was born!
Now, don’t get me wrong some of the technology that allows existing cable to run audio / video / data is truly epic. But again there are specific cable for the purpose as it has been designed to provide the expected and consistent performance as intended.
In between this new age of media converters you literally see (at least I do) in the field are people using the cheapest (same concept) say a balun from the lowest priced vendor!
When you couple this with $.90 siamese cable that uses CCA, 26-28 AWG internal wiring the current draw / voltage drop is too large to sustain over the long run and hence erratic performance and ultimately a hardware failure at the end point or supply chain.
This doesn’t even address following proper distance limits, quality termination points, and water tight glands.
I haven’t even touched upon proper wire routing and type of cable. Yet every day we see cable teetering on breaking open or about to short out causing a raging fire.
Every time I see more than 50 feet of cable all coiled up and not cut to length hanging in the rafters or ceilings I just shake my head.
These are the same people who take a legitimate media converter say a POE splitter buy purchase long dick dongs cheapest on AliExpress for $2.00 and wonder WTF as to why things don’t work or over the long term.
Your a cheap asshole that’s why . . .
Now, don’t get me wrong if everyone was made of money all of us could buy the best and never have to worry about stuff.
Wrong . . .
Because I’ve worked on hundred million dollar projects and the GC was a stupid twat and substituted hardware and cabling hoping to gain more profit.
Obviously this sort of thing isn’t that common but trust me the industry like any other likes their kickbacks, over charge, extra bill, and half ass something when they can.
The days of a hand shake and a persons word is long gone in 2021. The only thing that keeps these people honest is the courts, jail, and monetary losses.
Back in the day I thought what are the odds people will try to fuck with the government?!?
Sadly, this sort of thing happens daily in some form no matter how small.
Regardless, nobody serious uses existing wiring unless a dozen caveats are met or stipulated in writing. As the OP has stated he now owns a bag of shit because all they did was install a door bell!
Nine times out of ten your going to see clowns are us use the existing transformer that came with that 1970 door bell.
How and why would you expect a low amperage transformer provide enough current to operate a power hungry door cam that is asked to operate in the extreme hot & cold while recording 24-7-365?!?
I’ve yet to see a single person ohm out the resistance of the existing bell wire and and also measure the voltage with a DMM. Never mind cutting back a 1/4” of wire to expose and use (clean copper) wire for the install.
Don’t even ask if they bothered to put a dab of dielectric grease to promote connectivity and reduce moisture.
None of this even addresses the fact unless you invested in good network hardware and tested your WiFi. How in Gods green earth do you expect to see reliable connectivity on a door cam when said router is from Bobs ISP in the basement 50 feet away, two floors down, covered by shirts and socks???
The fact you never see a homeowner much less a tech complete a site check to validate the environment is quite telling.
If your going to install any WiFi device how about you wip put your freaking phone to see how the reception is!! That’s just a basic test because it’s not a true test because your going to find that new shiny door bell toy literally has the worst wifi hardware inside!
So based on the site audit you have what?? A great opportunity to up sell anything from a repeater, Access Point, to an entire mesh router!
Genius . . .
All of this avoids repeat visits, support calls, and endless removals.
Most of the time you can give Joe Public a pass because they are ignorant and hired you the Pro to advise, suggest, and install. So if Pro Bob hasn’t used any common sense and follows best practices these are things you will have to suffer.
End of Line . . .
Sadly, this sort of thing happens daily in some form no matter how small. 
