Oxygen is Oxygen. There is no difference between aviation and commercial welding oxygen except for liability insurance.

For a given tank, there is likely no physical difference, but the fill procedure appears different.
For welding, just fill is ok.
For medical and PBO, evacuate first is required.

If the previous user left the tank open for a while, there is a small chance of moisture but probably nothing else harmful.

I can get a big tank of pbo for a month from the welding shop for $35. The problem is I have to give them a week's notice so they will have it. And I can't go to a random Tractor Supply to get it.

For me, the extra hassle is worth not having to think about such an easily avoided 'probably'.