Yeah, I'd tend to agree here. I wouldn't let anyone mess with your radio.
These guys that do this are referred to as "Golden Screwdrivers". They'll claim to "peak and tune" the radios for a not so minor fee. Trouble is, they are usually guys that learned somewhere along the way to twist a pot, spread some coils, or generally fiddle around while watching the needle on a watt meter.
Honest truth is that RF power output isn't as important as many people think it is. Even if your 4 watt radio is only running a 75%, the 3 watts versus 4 watts isn't going to amount to anything noticeable. And, yeah, you could probably get someone to tweak it just right and get 12 or 15 watts out of it, but again, all this is is RF output. Usually it comes at the expense of spectral cleanliness, etc. Cranking the power on these radios sometimes just splatters signal all over the CB band. Sure, the needle on the watt meter is showing more power, but is all that power going where you really want it?
If you were going to do this, I'd really shop around and find a technician that's got the knowledge and tools to do it right. That would mean more than just an expensive watt meter. They really need to be looking at the actually RF emissions of the radio. Making sure it's on frequency, it's inside the channel it's supposed to be, and your increase in RF power is going where you need it to go.
Personally I don't see the point. Like I said above, the increase in RF power isn't what makes it work well. Put the money you'd spend on a "peak and tune" into better coax and a better antenna. That'll work better than the golden screwdriver treatment.