I bought some keys in TF2 early on, was fun and got some cool stuff. The cost didn't bother me much, as I've played a ton of TF and got it with the orange box. Maybe $20 total.

I'll occasionally buy stuff in mobile games if I'm enjoying them, why not? If they're f2p and it's helping me waste some time on the bus or whatever, it's no big deal. There are so few decent mobile games that I don't mind spending a little bit to extend the fun on the ones that actually are good. Maybe $100 total, but not more than like $10 per game.

That's pretty much it. I designed a multi-million dollar earning f2p game at a previous job so I'm well familiar with how far down the rabbit hole of spending you can get, and I always keep my total expenditure vs enjoyment and time played on a game in mind. But I also see right through most f2p schemes and it's not hard to evaluate if it's worthwhile or not... things like Fortnite are a total non-starter, and anything with generic loot boxes I look at with an extremely critical eye. If you're too lazy/inept to build microtransactions that are actually a part of your game rather than a poorly tacked-on money sink, I probably won't even bother playing in the first place.

The funny thing is, the combination of my disposable income and the fact that I work in the gaming industry and feel comfortable spending serious cash on games, means that I AM a potential whale. But the quality just isn't there... I haven't played a game that is worth spending $1000+ on, but I'd be happy to do it if I found one.