I'm curious if there are cards/events that are widely considered illegitimate or unfair? I had someone call me a cheater and resign a game yesterday because I played Inheritance. They said it was a hack and that they don't play with cheaters. I was pretty surprised and unsure if they were just being a sore loser or I was missing something and shouldn't have played it. I blacklisted them so they won't have to deal with my nefarious ways in an automatch again, but, then I kept wondering if I actually did something wrong.
Assuming what you say here is true, and the only thing you did was buy inheritance, I wouldn't worry about it too much. Buying cards (or card-shaped-things, because in dominion terminology Inheritance isn't a card) is never cheating.
The only unacceptable / 'wrong' things you can do are
a) deliberately insulting your opponent in chat.
b) deliberately stalling the game (thinking is ok, just making them wait for the sake of annoyance is not).
Fortunately the vast majority of players consider those two common sense.