I've not had a ton of purchases so it's not like I'm statistically bound to hit bad cases, yet I've run in the past into a major major issue with them, and their consequent handling was a total disappointment. I'm much more guarded since then but still use them, just factoring in a revised risk assessment.
Other than that, also various smaller issues. Part of it may be because I'm an optimizing buyer and their promo system has always been fragile.
Futile chat and email conversations are hardly a rarity, with reps that misunderstand or misread. Their lack of continuity in support also doesn't help in that regard (though sometimes it does help because you land on a better rep). But as long as nothing off-script happens they're definitely above average.