I wholeheartedly agree BB, UPS is a big rip off....I mean I've left personal items at friends' places in the US and they tried to charge me duty and handling and brokerage when I had them shipped up. I'm talking a personal cellphone here. Frickin bandits.
USPS IS the best, as said, IF there is going to be duties the charge is only 5.00 plus whatever the duty is.
For a complete list of items and the associated tariff go to the canada customs website and download the list. Many items are 6% some lower some higher.
Many sellers won't ship to a PO box so watch for that
Paypal is the most secure, they basically guarantee your purchase is as described.
You will have to have an ebay "confirmed" address for most purchases same as paypal. This way they can verify that you are actually the holder of the credit card and the item will be shipped to YOU not someone else. Many credit card companies in Canada won't confirm your address (see the paypal website for more info on this).
As stated, look at the seller feedback, if they've only sold 10 items and have 2 negatives I'd avoid them at all costs.
Watch for phatom bidding. There are a lot of sellers that have their friends etc. bid on an item to up the price. If you are bidding on 2 or 3 items from a single seller check the other bidders id. If you find they are constantly bidding on the same items as you are, stop.
Be knowledgeable about what you're buying. Know what you can get it for at retail as many times I've seen tools that are on sale at Canadian Tire for $9.99 selling for 20 bucks or more on Ebay (dummies lol).There are deals to be had, I typically have been paying about 50% retail on the items I've purchased. The best deal I've gotten to date was an RC gas powered car kit that was selling for 700 here when the package arrived it had a price ticket on it for 499 US and I paid, landed here with shipping, $150.00 Cdn for it.
Just be careful, follow your gut, if the deal seems to good to be true, it probably is!