I’m told buy a fuel guy this is ok, in fact you can get an STC for it.
The issue is to ensure you don’t get fuel with methanol as it can strip your seals.
So buy it from a reputable supplier as dishonest suppliers mix fuels.
The key is, add water to a jar and mark the level with a texta. Add the fuel, shake it and let it settle. If the height of the avgas is higher than the original mark, you have methanol....use it in your car, not your plane!
Shandy it with avgas and only in one tank....keep one tank always for avgas only, for takeoff and landing.