I have only had issues with knifecenter, who seem to allow an unlimited number of preorders even though they know they won't be able to fulfill them all. No issues with others, although I haven't done many. In general I've had great experiences with Knife Works, so I'd trust them to do a preorder for sure.
NEVER PREORDER REGULAR PRODUCTION KNIVES! They'll eventually be in stock and plentiful, and you'll almost always overpay by doing a preorder. This may go without saying, but I did it a long time ago and always mention it when preorders come up.