My understanding is that you pay for each bid you make. Keep in mind that, even if you don't end up with the highest bid, you're still paying for each bid you made. IIRC, the bid increments are ridiculously small too.
dealdash is HUGELY misleading on their ads. They make it sound like you can get all these high price items for pennies on the dollar, but you end up paying through the nose for every single bid you make. I've known a few people who used it and after a couple auctions bailed because all they were doing was prolonging an auction that drove the price up to just under retail anyway. Throw the cost of how many bids they made on top and it was a total waste.