is there any way to retrieve photos from a 5c that has gone into recovery mode?

No, by the time its in recovery mode it's too late. The contents of the phone are gone. Did enable any of the ways that Apple provides to back up photos?

• Backup the phone to your computer
• Automatic daily iPhone backup to iCloud
• enable Photo Stream
• Copy photos to your computer using a USB cable and a compatible photo management utility on your computer
• Enable Photo Sharing
• Enable Photo Library backup

OR any of the 3rd party photo management solutions, such as Google Picasa, Google+, Facebook, Shutterfly?

OR any of the cloud sharing services such as box.com or dropbox?

If you have set up any one of these your photos can be retrieved from it.

I know that it's seller constantly spams the forum, in spite of being told hundreds of times to stop, and its spam posts get deleted regularly. Many of the posts disguise what is being offered with a hidden link.

I would not trust any product whose marketing plan is to spam support forums.

In addition, if a phone is in Recovery mode there is nothing on it to recover with any product.

Sort of reminds you of MacKeeper and Zeobit and we all know how much they are trusted.