The padlock is a sign that the website has an SSL certificate, which allows the information you exchange with the website to be encrypted. It's really only necessary for when you're paying or logged into somewhere (like your bank), not for browsing.
The website does not take payments, rather hands off to Paypal. Paypal will ensure the transaction occurs in a secure environment, aka SSL.
In terms of marketing, the fact that they don't tell the user about how secure the information is with the seller and explain the security aspects of using Paypal is a massive weakness.
It does however look that the Purseforum users consider this site okay. I have no personal experience with the site though.