Use Priority Mail International boxes that are free from the post office. They cost more to ship but are worth the few bids you might lose from higher priced shipping.

Always insure & add tracking for packages sent overseas. It's a few extra bucks. If the buyer cooperates by sending pictures and such, you can file a damage claim with the PO and get a refund most of the time.

Tracking is not offered on Priority Mail Envelopes so avoid these if you're shipping high dollar items.

First Class is acceptable to places like Canada & the UK in my experience. Insured and tracked of course.

Hope that helps.
Arg