Welcome. I see nobody answered you on this so I'll just mention a couple of things that I've found from watching the classifieds.
Know who you are dealing with. If they are registered users for a long time then the chances of them being reputable are better.
They should answer in a timely fashion and respond to all your questions.
Being in Canada is a disadvantage as shipping can be a problem, and pricey, some guys would rather not bother to check into it so you need to be aware of how you want it shipped and such.
Money orders are popular but you may find PayPal to be a better choice due to the delays in international money orders.
Clear communication is the key to a good transaction. Phone numbers are nice to have as email seems to 'vanish' depending on the buyer/seller.
we have implemented a feedback system in the past month so there is not much information yet but we hope to have ratings for the regular users on the classifieds.
That's about all I can offer as I don't buy much via the classifieds, but then again as the administrator I tend to get my emails answered.
watch for scams - https://www.camaros.net/classifieds/scamalert.html