You would need to question eBay
Fellow buyers and sellers cannot explain 'why' when you come in all huffy and give us zero information to go on
If you have not been given any notice at all, how do you know your account is restricted as such?
The seller in question may have you on their blocked buyer list
Or the seller could have limits on how much/many a buyer can buy from them within a certain time frame
It could be a glitch
Have you reached your buying limit?
