Should i buy a 3 wheeler atv?

I found one that runs great for $530 its a honda bigred

They are fun to ride in the street just after the snow plows cleared the roads.
Back to your question - "Should I buy it?"
They are so old, parts are almost impossible to find.
Search the web to see if you can buy stuff.
That will answer your question. Those things were killers! That's why they quit making them. There's an increased risk of turning over, especially on a slope. But it is your money so knock yourself out (perhaps you should avoid that). Do what you want with your money. Old 3 wheel ATVs had a hard to turn and rollover record in many places, that got them banned for new sales. Some still around and working yet as intended, driven by reasonable riders so not completely dangerous. Parts availability has been noted

Those things were killers! That's why they quit making them.

There's an increased risk of turning over, especially on a slope. But it is your money so knock yourself out (perhaps you should avoid that).

Do what you want with your money. Old 3 wheel ATVs had a hard to turn and rollover record in many places, that got them banned for new sales. Some still around and working yet as intended, driven by reasonable riders so not completely dangerous. Parts availability has been noted