It depends on soooo much. Most notably what factions you are playing and whether you can deckbuild. Though the stats (thousands of games on OCTGN) show that the core factions are all extremely evenly balanced (almost absurdly so). As a general matter, Criminals get rich if you leave HQ exposed (and Archives if/when they get Sneakdoor). I leave R&D unprotected if needed early to avoid Crim getting easy money. (This is also why I run Maker's Eye in my crim deck but that's metagame stuff
). If it's Shapers, Kate is slow as hell. Attack her early, especially when she's low on credits from putting out all her expensive bloatware. Anarchs really shouldn't be getting rich, that's not really their bag.
Get protected first, but then try to score a quick and cheap agenda (doing this with Accelerated Beta Test or Priority Req can give you a huge edge). I've actually been thinking a lot about this and yeah, stuff like Magnum Opus can be a giant pain if you just let it sit there. But if your opponent is trying to build an indestructible rig, that's really your time to sneak an agenda past him (hopefully your second one at this point). Finally once you are getting into the dregs, this is where traps can come in really handy. Again if you are running against a monster rig, stuff like Aggressive Secretary with two tokens on it can pretty much spell the end for the runner, no matter how rich. You can also go for a Scorched Earth deck, which can be unstoppable if you get the right cards.
Also again if the runner is just piling up money he's missing out somewhere else, probably in setting up his icebreakers. It's your job as the corp to spot that immediately and exploit it. Whenever I see people piling up money in a way I can't immediately stop, it really gives me a sense of urgency. Yesterday I was able to pop a guy's Magnum Opus and Gordian Blade with Aggressive Secretary because he was rich and reckless, for example.