My rule is if they're available on the ask....grab them.  If the ask is showing 50 lots available, and if you want to buy 5,000 share or less then my own opinion and something I've done many times...just slam a market order.  It may be that the house showing those 50 lots on the ask, they may not actually have them, it could be a bluff meant to foment an impression that  there's lots of shares available that sellers are looking to dump.  But if they put them out there, short or not, they're available.

Right now i'm seeing RVXCF showing 2,100 lots bidding $2.97 and 1,200 lots asking $3.02