Cheating in Tichu, online or in real life, runs into the same wall: it’s just not fun, not rewarding, not worth it. Plus, you’re often playing with people you know, and the BGA Tichu community is small, active, and experienced, so also players know each other to some degree. And in some ways, catching cheaters online is probably simpler than offline.
On top of that, Arena and many regular games use random seating, so even if cheaters tried to collude (e.g., one losing on purpose to boost another), it’d be tedious, obvious in stats, and a waste of time.
Some cheaters exist, but in my experience, they’re rare. It’s usually clear after one game, and I hit them with a red thumb and spread the word. This is quite effective.
I won’t list the telltale signs here, I’d rather not play a second game to find out someone’s cheating. But if you want, I can share a few recent names privately. If you’ve played a bit of Tichu, you’ll likely spot the red flags yourself.