You collect what you bet minus whatever vig odds a book ahs. if you bet $100 at Pin and the line is -7 -107, then you would collect 93.46. if you lose, you only lose the $100 you bet. So in essence they are charging you $6.54 for that winner.
You can only lose what you wager, whether that be $5 or $550. Whatever you have at risk is what you can lose. But when you win, you do not get the full amount back, you get that amount minus the vig odds, if they are negative that is.
When you bet an amount, technically you should get that same amount back, but the books have to take their hold, and that hold is determined by the odds on the vig, whether it be -110, -107, -105, -120, or whatever.
So when people bet X amount to get X amount, they are not really paying the vig up front, they are simply betting more. The vig is going to come out anyways, if you win, whether it is an even number or not, it doesn't matter.