I built this site for a client, using google sites.
Biggest problem is checkout. The only google gadget I had for checkout requires google wallet. My client is so frustrated with google wallet, that he no longer accepts online payments, and requires his students to bring a check to his classes.
I feel this is a huge failure on my part. I suggested using google sites (price was right, and traffic is very modest).
I am not certain, but I think there is now a gadget for using paypal.
Any advice appreciated.