Best show for begginers in Canada is NUPHILEX in Montreal (next one is by the end of October).
In MY experience - coins in shows are not over-priced. They are fair priced and you can always negotiate with the dealer.
I am not a dealer - I am a collector. That said, I have to say that us collectors and sellers want to make a good deal - buy cheap and sell high. It rarely happens. What usually happens is buying fair and selling fair. The exception is when you are a specialist: then you are capable to spot something that the dealer did not see and buy really cheap (as I did many many many times).
Now replying the original question: many collectors exhibit with the intent to showcase and sell - it does not harm if you ask. You can do it upfront because the exhibit is independent from the bourse. I exhibited my coins a few times and received offers for all the exhibit and for one or another coin - hard to explain that they are not for sale because people are used to the trade. I have friends who NEVER took their exhibits back home - they prepare them to sell (usually doing a good deal - because those lots are hard to put together and document)