Has anybody used Skip Tracers?

Has anybody used Skip Tracers?

I send my vacant house addresses to my Title Company and they send me a Title report on each address. some of the owners mailing addresses are listed as the same as the vacant boarded up junker. Of course I mail to that address but a good percentage comes back as undeliverable.
At that point I give up and move on. I cant help but think of all the money I'm losing by not going further and hiring a skip tracer.
Has anybody used these companies? Do they work? can you share their name and contact info? Oh yea and the price. I found one that charges 68-$75 buks pr name. I suppose that wudnt be nothing if you consider the potential profits to be gained.

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Rando