This might violate GPL

Would it? It would almost certainly be legal to refuse here in the UK. If a shop mis-prices an item they can refuse to sell it. What they CAN'T do is reprice it upwards at the till, but if they put a £10 tag on it instead of £100 they can withdraw it from sale. Most shops however would honour the £10, write the loss off, and rapidly go and reprice the shelf, but they are under absolutely no obligation to do so. (Repricing at the till is treated as "making a fraudulent offer", and while shops do do it, if their victim is a Trading Standards Officer, they are in for a world of hurt ...)

So if Red Hat said to a prospective customer "you've acted in bad faith (broken your contract) before, we don't want to deal with you", there is absolutely nothing the prospective customer can do about it except walk away - Red Hat could even threaten to bill them for wasting RH's time and they would be completely within their rights.

The government does not get involved with private contracts, unless the judiciary is asked to rule on a broken contract (or other such things as is a contract legal ...).

Refusing to sell is basically policed by the reputation damage such a refusal would cause. Which is quite often minor, especially for the big players ... (provided they don't do it too often).

Cheers,
Wol