I was working on a project where users can upload files, and I got frustrated by the lack of options for preventing my website from becoming a vector for spreading malware. My choices were to use something inadequate like ClamAV with it's terrible detection rates or spend a huge amount ($10k+) with a yearly subscription for a major vendor that offers an API or SDK.
I decided to build my own AV scanning API instead, though I only managed to get one commercial engine integrated into it, with ClamAV as a backup.