This isn't surprising. It'll take a few more years for the mainstream to catch up. It's still oftentimes hard even for technical people to understand the exact application of cryptography in Bitcoin and understand why the system is very secure. It takes a lot of work even for programmers to fully comprehend BTC. A non-technical person who is exposed to Bitcoin for the first time would be more likely than not to think it's a scam.

We just have to prove it to them by developing an actual economy that people use.

Whitelists are better than blacklists. Google everybody you're about to purchase from and try and make sure (to the best of your ability) that they're reputable. If they have some reviews online, if nobody is calling them a scammer, you're not perfectly safe, but you'll have better odds by choosing somebody with a good history.