Acceptable? That's a frame of reference. Is it widely practiced on the internet, on every social channel? Oh, yeah, it's everywhere. They are not doing anything different, but they are executing the ads rather well.
I am curious how far they are going to grow before they turn the ad machine full throttle, and whether or not that will have a huge adverse effect.
We all kind of know that Instagram is a giant online store for everything, at least it has been for a few years now. Unsplash contributors seem to think that free will last forever. It'd be very interesting to see if they stay or leave.