As a rank beginner I caused myself loads of grief by trying to turn odd bits of scrap. When things go wrong, is it me, or the lathe, or the cutting tool, or the material that's causing trouble? The beginner is likely to be baffled.
Most of my scrap turned out to be difficult to machine and DIY store bought metal is pretty poor too. Not using known materials delayed and confused me. It was a false economy.
Now I'm more experienced I know better what to expect from scrap and have been more successful using it. Even so I almost always buy new – it just saves time and bother.
None of my local scrap dealers let people wander around.
Cheers,
Dave