Yes, I am that guy. I made my living being better then the next guy at automotive electrical and electronics.
Now that I have retired I think I'll share a few of the nastier things that I have done to earn my money. None of them are illegal.
I used to put in kits for dealers to turn off your car if you started getting behind in payments. I liked to do them and I made it my job to befuddle all but the sharpest techs by installing them so they keep the PCM from getting the signal from the passive anti theft instead of the starter circuit. Factory passive anti theft systems make mental cripples out of most guys that dont work at the dealership. Methods of repair are New PCMs and start replacing parts until it works. Which will not fix my method of using these devices, simply putting it inline with the start lead to the starter solenoid is easy for any tech worth his salt at a corner repair facility because the starter wont turn.
When you disable the signal lead from the passive antitheft system the PCM does not get the ok to run tone so it doesn't trip the fuel pump relay. When the car is cranks there is an additional circuit that powers the relay during cranking so what you get is a car that will star but stalls. This will bedevil all but the most competent tech. Even then it may take him a while to figure it out.
When I put these systems in a bury them, they are not obvious nor easy to find. I don't use crimp connectors, these are hard soldered and combined in to the cars own harness.
So if your in that car you bought at a buy here pay here dealer and your behind on the notes... Think of me.
Since these units all have GPS once the car is stopped simply send out the tow truck. You can see the car location on the internet on a map. It's more fun to install than a stereo.