Trust is a personal decision based on too many factors for anyone here to endorse that you go and buy from random sellers on any given platform, lest they be held liable in some way for deals that go bad.
There are trustworthy sellers on Instagram, and I'm sure there are snakes in the grass. You need to just go explore it, see who is on there, do your own due diligence before sending anyone money, and you'll be fine.
Just keep in mind there is no recourse built into the platform, only through third party stuff like Paypal G&S payments etc.