PayPal is a bit of a double edged sword; you'll be charged for customers buying through Paypal, but you may gain more sales. A lot of people see Paypal as trustworthy; especially with the money-back guarantees and whatnot that it comes with. (And because it's so popular)
So, while you may get charged a % to use it, it may help you attract customers at first. Especially as you're a new store. Personally, I'm much less likely to trust a new store. If I had to pay via credit card, I probably wouldn't just because I'd think it would be more difficult to get my money back if the store turned out to be a scam or something. If the store had Paypal, however, I'd be much more likely to purchase from the store because (although there's absolutely no reason to and this is jsut my opinion) I'd trust the site more, buying through Paypal doesn't require me to get my card and write all my details out and I know I'm covered to get my money back if the store does turn out to be a scam.
Just some food for thought