If I purchase a burial site and at a later date decide to go to Greece to be buried, will I be allowed by the foundation to sell my grave sites?
Yes you can sell your burial sites as long as it is to another Greek Orthodox Person.

Can I have a head stone on my grave instead of a flat marker on the ground?

Yes you can have a stand-up 2 1/2 foot head marker on some grave sites only. All the grave sites in the Greek Orthodox Section are not allowed to have stand-up head stones. Before you buy you must let us know that you want a head stone instead of a ground marker.

Can and will the Foundation help me sell my burial sites to Other Greek Orthodox People if I have to sell my burial sites? 

No.  The foundation will allow you to sell your burial sites to other Greek Orthodox people, but since we are a non-profit foundation and not a broker, you will have to sell them on your own.
Does the foundation accept major credit cards for donations and/or the purchase of grave sites
Yes, the foundation accepts Visa, Mastercard and American  Express.
I have (2) two burial sites at Rose Hills which I purchased some years ago. It is not in the Greek Section but it is in  another section. Can I trade those two burial lots for the equivelent number of burial lots in the Greek Orthodox Section? 
The answer is No. You will have to sell your two (2) lots that you have on your own or through a bona fide licensed broker, and then you can buy the 2 lots in the Greek Section from the Foundation. (Or vise versa: you buy the 2 lots from the Foundation and then sell your other two lots.)