So buying several copies of a price error game will now have Valve block your IP for purchases

The "An unexpected error has occured" thing is a soft lock used by Valve to prevent you from buying a lot of gifts ^_^ It's been happening for a while now, it started becoming a problem in October. It kicks in if you exceed a certain limit when buying giftable copies - I don't know the exact numbers, but you have a certain purchase limit per day and another limit per week, whichever happens sooner.

When you get hit for the first time, it lasts for 24 hours. The second hit flags your account and the cooldown is 1 week. After that each lockdown lasts for 1 week, I've also heard of the one lasting for 30 days, but I can't confirm that info.

The soft lock should only prevent you from buying gifts, purchasing for yourself should work.

Uhm so, you cannot buy as a gift from client\browser, but you can from phone, isn't it ?

If that happened during a steam sale or something many people could get banned for gift shopping and thinking it was a legit sale. It's so stupid, do what every other store does and honor the sale and then make a correction.

I think it's the correct thing to do, you shouldn't try to profit from something else. The thing is it would suck if you weren't aware of the price error but you bought the game for yourself anyway.

"We screwed up on our end, but we're banning you anyway"

Yeah, sounds like Valve, lol.