There are many selling sites ...Ok I will share my experience...I will give the general tips instead of giving you a particular site...
first do a Google search and find website that has the product that you desire
pick a legit one from it...
To check whether a site is legit usually, I do follow a simple checklist to see how well they do, especially when I need to part money with the site;
1) Does the site have a current SSL certificate?
2) Use http://www.whoisxy.com/ to check the whois information and check whether the contact information matches with the one in the website.
3) In the domain contact details, is there a valid email address.
4) Is there a valid phone number visible, and does it work ?
5) Go through review about them using Webutations.net and check whether they are scam free.
Purchase a small priced article and if it is delivered safely and promptly then you can purchase your favorite product from the picked website...