"Artists Beware"

I have an opportunity at a one-off job as a colorist for an image. The thing is, this is being decided by having people interested fully color a "test image". The questions I have are:

1. Is this a common thing for people looking for colorists? Or is this a huge red flag that the person is trawling for suckers to color the "test image" for free?

2. If I do go through with applying, would I best explain watermarks etc to the possible commissioner? I don't want to sound accusatory in case this is legit.

Something else I thought of the other day that I wouldn't mind getting some feedback on especially from the artists. Whenever I ask for an update on a commissions, I sometimes get a response about them not having inspiration to draw/write which I take to mean they are in a supposed art block. I often hear lots of people saying that its just an artist excuse to be lazy but then when you have lots of stress coming from outside life, it can be hard finding the inspiration to draw/write a commissions. What do you guys think? Is it a plausible explanation for delayed commissions?