It is the same with ATVs and sleds. When I found the used sled I bought this past February, I jumped on it immediately. By the time I got there to look at it, the guy told me he had 8 or 9 other calls after me and several asking that he call them if I ended up not buying it. I had earlier lost out on a deal when a guy had two to sell and the first person to come and look bought both.
They try and steer you towards their financing but I don't think they can require you to use it though, can they? If they give you a better price by using it, take it and then re-finance with your preferred lender. I've done that before.