Alfa, would you want to only convert links in the custom fields, or also run Insert on content within the custom field (Insert links into the text).
I will explain the situation to see what possibilities you can offer: My members add listings for products and companies into Review Management System (RMS) by @Bob
Custom fields in RMS work exactly the same as in XenForo Resource Manager and Showcase
. (also by Bob)
How I have it setup is that the member can fill in a custom field by entering a link. I use custom fields value display html to turn that link into a BUY NOW button. This button is displayed prominently on the product listing as well as the category listing and in various widgets.
So to answer your question, the simple solution would be to have the link turn into an affiliate link.
However, if somehow possible, it would be great to give the reader multiple affiliate links to buy from. For example, lets say the product is a book. Instead of just showing a button linking to Abe Books (which we do now), it would be great if we could also show links to Amazon, Barnes & Nobles, etc. Then the reader can decide for himself and pick the vendor that is most likely to lead to conversion.
For books we can use multiple custom fields to do that because there are just a few major book stores. But for other product categories there are many possible vendors. So finding an automatic way to generate an affiliate link would be great. I dont know if this is somehow possible.