I use PayPal Standard. If a payment is made to my site from a credit card without logging in to PayPal account, the user is returned back to the page that initiates the payment. The user is prompted to make again the same payment.

The option to pay without logging in on PayPal is controlled by the following PayPal option:

Profile->Website Payment Preferences->Turn PayPal Account Optional - On.

When a payment is made with logging in to PayPal account, the user is returned correctly to the address specified at:

Profile->Website Payment Preferences->Auto Return for Website Payments.

Thanks. I opened a support ticket with PayPal Merchant Technical Services. Here is their reply:

Thank you for contacting Merchant Technical Services.

You will need to add rm=2 into your cart code. It will force PayPal to POST the return details to your landing page without adding the '?merchant_return_link=Return+to+Your+Domain&form_charset=UTF-8 ' to return address .

Here is a sample how to do that with PayPal button using the rm=2:

<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="D5UUYFE6PTAPU">
<input type="hidden" name="rm" value="2">
<input type="image" src="https://www.paypal.com/en_US/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>

I hope this helps. Please let me know if you need further assistance.

Regards,
Sh.
PayPal Merchant Technical Services
PayPal, an eBay Company

We made the change and added rm=2 in the redirect to paypal as paypal support instructed. Please send an email to support@smithcart.com and we will send you a new dll.