Look at it like this. Any good salesman would prefer that you try it on with the 1% chance that you will buy, rather than not let you try it on. You should never feel bad about trying something on. But would they want you to try it on if there were less than that 1% chance? And should you take their time away from other customers that want to actually buy in the store? As mentioned above. we have gone through this ad nauseum, with clearly some feeling its OK and some not. I think that the correct way to approach this is why not be upfront with them and tell them that you have NO intention of buying here and just want to use them for sizing so you can then let them make that decision of do they want to even try, But its probably unfair to lead them along that they are making a sale when you have no intention of actually buying in the store. Isnt that why you are asking here? Ask them...You will have done the right thing and they will have that option if they want to pursue attempting to win you over.