Every card is slightly different in how it qualifies what does and doesn’t constitute business spend, so it’s hard to say with any certainty. However in my experience if they deem it’s business spend you’d be neither eligible for it to count towards spending criteria for bonus points, or to earn points on the spend with most card providers.
When you apply for the card there is usually some sort of painfully long fact sheet or PDS type document which nobody ever bothers to read, but in the depths of it somewhere they will clarify what they deem to be business spend.
In answer to how strict are they on checking this in practice not very I’ve found, but you’d have to weigh up the risks vs rewards. How big of an impact would it be to you if you didn’t get the points and were then ineligible for sign-up bonus’ for the next 18 months with nothing to show for it? If the answer is very, and you’re not likely to qualify for the spend through personal spend then I’d suggest seeking a different card.
In practice you’d likely be fine as I have frequently put the costs of flights for business purposes on cards and it’s been counted both towards a qualifying spend for bonus, and to earn points with many banks. However I’m guessing they would be within their rights to discount it and not award you the points if they audited your spend and noticed. You’re spot on about the fact that you’d be much more likely to get caught out if you put thousands for a professional development course or equipment on the card because that’s fairly obvious, but I can’t imagine how they would pull you up on a simple flight booking; people buy flights for themselves too.
Hope that helps!