Reputation is a mechanism to escape the 'market for lemons'. Eg I know that Miele sells good stuff, and they are defending that reputation by continuing to produce good stuff, because it allows them to charge more.
Gresham's law only applies when someone forces you to accept both moneys at par. Historically, people would require discounts for the bad coins, when they could.
That's also why coins meant for an international audience where consistently of high quality, even when the domestic coins of the same issuer where being debased. (The Spanish dollar was a very good example of this. That's what the Americans used to use.)
And that's exactly because while you can force your own subjects to accept your coins, you have to convince the foreigners. Reputation is key. No 'bad money drives out good money' here. Just the opposite.