If you are not selling downloads, you can just go to Seller Admin > Account Preferences and enter a Common Thank-you Page URL where all buyers will be redirected, or you can enter a specific URL for each product by enabling Redirection in the product's settings (in this case, you should NOT add any thank-you page customizations). Note that product-specific Redirection counts as a "digital product" (as this is usually used to grant access to premium content), so you would need to subscribe to a plan level that
If you are using our download-delivery system and also need to redirect to a page on your own site, then you would need to know how to program some custom scripting, to display the content of our thank-you page (including the unique, expirable download link(s) we issue to each buyer) inside an IFRAME within your site's common thank-you page, as described here:
http://www.e-junkie.com/ej/help.redirection.htm