Before you let them put anything inside the tire, find out what it does to the warranty of the tire.Michellin will void the warranty.Goodyear reserves the right to void the warranty if they think the added stuff damaged the tire.Lots of people have advocated using golf balls & some have had good luck with that, but that is not for me.If powder is used, you must use DRY air to fill the tire since moisture will cause 'clumping' of the powder making it ineffective.Personally, I'll heed the advice of the tire maker over the opinion of the installer. But that's just me.My choice is to buy the proper tire for the job & have them spin balanced along with a proper alignment.Good luck.