Data center proxies are not always the same. You can use them and never get locked or use them and get locked most of the time. And the locks are what you do not want. If you making higher level accounts it doesn't bother you too much to unlock some of the account, but the thing is that you will have to put an email on the account thus it could impact your sales.
Regarding country I guess most people prefer USA since USA proxies are cheapest and easiest to get in general so many people use them. If say you create account on France and sell it to someone who always use USA IP he could get insta locked. Also everything depends, if you selling max stakers, or 70/70/70, ready pures or whatever which could be considered more to high-end part it could not bother that much since the person would only need to unlock it one time and start using it. But buying 10 accounts for botting lets say and having them all insta locked due different country ips would definitely be a problem.