Originally Posted by
Kimmo
I'd say there's a good chance it's square. You should probably file the paint off the faces, at least.
You can probably get an idea how straight they are by colouring over the ends with a permanent marker, half-tightening the cups and then undoing them again to see where they've rubbed off the ink...
And if you take the bare frame into a shop, they shouldn't charge you much to face the BB of an ally frame.
This is good advice.
Just as an additional useless comment - our shop prepped and built a $14,000 Italian machine for the Expocycle last year. The BB needed facing because the clear coat covered the external bearing interfacing surface but surprisingly enough - the BB had to be faced to bring it within dimensional tolerances too. Check the specifics for your own crank and you'll see some pretty hard numbers.
So if they were initially off on a hand built frame for a $14,000 bike - I wouldn't count on them being acceptable by default on anything mass produced with a much smaller price tag. But as noted - cartridge BB's and BB30 configs have slightly different tolerances.