I have check the site out the front page looks very nice. The theme looks very nice but when i view a item on your site it then all goes down hill. Ill give you a example your selling a item called "EBook - Make money fast!" you click it and it then takes you to a white page with the title and a buy now button. Maybe you should use the front page theme for your buy.php has well ?
I have also noticed your running your paypal buy buttons on sandbox ??
I have also noticed your running your paypal buy buttons on sandbox ??