I recently (today) went to Sam’s Club to purchase a right front tire to replace one that developed a sidewall bulge from a suddenly huge summer pothole. The sales person said he had to look at the tires, and upon return indicated that I would need to buy a pair, since the difference in tread-wear would be too great. He then went on to tell me that they would have to install them in the rear and rotate the rear tires to the front. I asked why and he proceeded to tell me that during a turn, the rear wheels could slip causing the car to go into a spin.
I protested saying that the drive wheels were more important, with respect to traction and that I would prefer them on the front wheels. I asked what they would do if it was a rear-drive vehicle. He indicated that they would still install them on the rear wheels. I asked that they install them on the rear wheels anyway. He said I would have to sign a waiver absolving them of any problems this might cause.
This has been discussed in depth, you can use the search feature to find the posts. Basically your rep at Sam’s Club is correct. And the reason stated is correct as well, rear tires with low tread can break loose and cause a spin out on FWD and RWD cars and that’s why new tires go on the rear wheels when you replace in pairs.
He may also be correct concerning replacement of 2 tires at a time. It depends on the mileage on your front 2 tires at the time you hit the pot hole. If you are more than half through the tread life, it would make sense to replace both front tires and have the new ones put on the back. And get a 4 wheel alignment.
If you live where winter traction(ice/snow) is a concern put the better tires on the rear. Otherwise when you stop or corner you will find the backend swinging around since the tires with more traction stop or grip first and the rears keep going since they have less. Spins with FWD are much more difficult to recover from.
This true in wet conditions but not as pronounced.
If you live where winter does not happen often I would not worry about it as much.