ok, maybe it is, but lets talk about practice, not theory. You say it's common. Have you tried it? What is your experience and the results? Did you have any tool to catch "moving lines" ? Do you know anyone who takes advatage of moving lines ?
I'm limited to basically nothing at approx 150 books :-) In tennis, that leaves me with just pinnacle, SBO and IBC. For exchanges, only matchbook - can't even use betfair because of premium charge.
If you want to know: sure, steam-betting will work, until you lose the account - bookies hate steam, because it gives them severely lopsided liabilities, and people doing it aren't going to lose.
Moves past 10% or so have heavy +EV at the original price, because they're incorporating new info into the market (usually injury, sometimes form). In other words, there was value at the original price - bet value at the appropriate stake, you'll win long term.
That's not just theory either, I've got all the market movement data on atp/wta/challenger moneylines since 2005. Openers, closers, and everything inbetween. Also totals/handicaps since 07, and more spotty coverage of correct scores.