My friend recently got his '03 Kodiak 450 back from the local dealer for a tune-up. He had brakes done, aftermarket skid plates installed and they realized that whenever he first bought the quad, he never brought it back in at their recommended mileage for the "valve adjustment". He was about 1500 miles overdue supposedly for this procedure. The quad runs great however, but he had them do it anyway. He got it back and did not notice a difference in power or anything AT ALL. Is the valve adjustment that all the dealers recommend a legit service or is it just to get you back into their shop and put your money in their hands?

 

Its not that simple. Its almost the same amount of work to check the clearance, usually it takes about 5 minutes more to do the adjusting. Unless you have shims to deal with, then it can take much longer.
It is necessary to have the clearance checked. Any number of things could cause them to be incorrect, from wear, to improper first adjustment at the factory. But the reality is, almost all motors are found to be in tolerance, at the 100 mile mark, and even 1000.
It isnt something that is difficult to do, especially if youre just checking the clearance. Then if you find them out of tolerance, you can decide to do it yourself, or take it in.
Unless they were alot out of adjustment, you wont notice any difference in driving it.
But it is legit , to do the checking.