One of the things I've learned to do when buying fabric:
I try to remember to check to see if the fabric looks like it's 'straight' while it's still on the cardboard.
Is it printed on-grain? If it's printed off-grain, I don't even bother to take it home.
Has it gotten pulled 'off-grain' in the manufacturing and packaging processes? It may or may not go back to being 'on-grain' after it has been washed and dried. (Doesn't matter who the manufacturer is/was)
The cutters will probably cut the fabric perpendicular to the selvage edge or fold - regardless of what the actual fabric grain lines are.
Exceptions that I've seen. I saw someone pull a thread on an expensive silk to get the cutting line, and I've seen cutters cut along a thread on a woven plaid.