The scale of this on the thread is astonishing. I hired in the past through marketplaces. One particular candidate started strong but then his productivity began to taper off. Camera off in more and more meetings. Less availability. And this was a full time position! I haven't been able to prove it, but a very similar profile photo showed on LinkedIn as working full time for a different company. Whether or not he was working 2 jobs, more, or even being a face of a dev shop, all are possibilities. All I know is this individual was not just working full time for us.
I was at a remote company last year and hiring (was lead, building the team) and right before one interview, I reviewed a resume and saw that there were.. 2 jobs for the same time period.
The best way to get the truth is to make all answers acceptable.
me: "So, job A was a 40 hour/week job, right?"
him: "Yup"
me: "But you were also doing work for job B then right."
him: "Yeah, basically"
me: "So you basically did job B whenever there was some slack for job A?"
him: "exactly."
I was dumbstruck internally and then just wrapped up the interview politely and let him know a couple days later that it wasn't a good fit. No use alerting him that he should change his resume (for other possibile employers..)
I don't see an issue here… He was completely honest about working two jobs at once, to the extent of putting it on his resume.
Surely you'd have followed this up with some questions about how the contracts for those two jobs were worded, or that you'd expect someone to be working full-time for yourselves and wether that would be acceptable?