Is a link to PepFX required if I buy your application? No, it isn't.
Can I modify the design of the application? We don't sell our source files, so you can't make any modifications yourself, however we can modify any part of the application in agreement with you, so you have a custom version of the application on your webbsite.
I am not familiar with Flash. Can you put the necessary files on my website? Yes, absolutely. We will need the FTP information (and if the application uses a database, then the MySQL information)
Is there a return policy in case I don't like it after I buy it? No. Once we deliver the files we have no control over them and their usage, so returning the money would mean giving away freeware.