Ouch that hurts. Your experience is one of the reasons I'm not fond of Paypal as a payment option.
Being Canadian or having a Bow shipped here provides some extra attention to details, so I generally shy away from social platform Buy & Sell Groups and stick to reputable Forum Boards, Archery Shoppes or Bowyers
However, before I commit to a deal I try to do some background checks on the seller ie; post count, recent activities and reputation etc to ease any doubts. Hard to do on the social platforms like facebook etc.. Once all of that has been done, I always offer the Postal MO or Intl MO is U.S. Funds as a payment option over Paypal due to it's traceability.
Having said all that, I did have an experience with a reputable Bowyer in the last two years, where an order was placed, deposit confirmed then all communication became sporatic to non-existant. I waited a year and a half before I was finally able to get in contact with the new Bowyer and basically give up a fair chunk of change ($400 Canadian at time of conversion rate) I had deposited initially because of the bad tatste I had with the whole experience. Even following my own rules above, i ran into a situation that shouldn't have happened even with a person having a solid "online" reputation. Not the new Bowyers fault and they were more than willing to make the situation right, but based on principal I won't be looking at that particular product anytime soon.
In the end it's always a risk, communication and gut instinct are key. If you have any doubts, it's better to walk away.