What caveats and hitches about airline seats should a flyer beware of? [closed]

I have long legs and thus for my upcoming flight to Canada, I want to book seats with extra legroom or exit row seats, but thought to Google and fortunately found this warning regarding Virgin Altantic:

If you pay to have a "legroom seat" (i.e. exit rows) be aware that those seats are more narrow than a regular economy seat. >>

True and not mentioned generally, worth knowing, but again, the same on pretty much any other airline.

So what should a flyer foreknow before booking? What do airlines conceal or misrepresent? Sadly, I'm destitute so am only considering economy class.