No, you just sell or buy for that price that you desire, ie. you make your own offer and wait for a sucker who is willing to take your offer...When shorting a CFD, do you pay (sell) at the BID price and sell(buy) at the ask price?

A CFD is like any other financial instrument, there's a bid and offer price. If you want to guarantee short, sell the bid, if you want a better price but no guarantee of a fill work an offer. Vice versa for longs.