[jb9]

If they are not offering you a contract (i.e., you are an 'at will' employee), then I don't think there is a problem with accepting now and continuing to look since they aren't really guaranteeing you anything.

If you get a better offer, just tell them "I'm sorry, but...". They won't be happy, but they'll get over it. Be professional about it and they shouldn't hold any long term grudges (in case you ever want/need to do business with them).

And if they really want you, maybe they'll make you a better better offer.