I happen to have a brand new, unused Nokia 6300 as a spare phone. There are no issues with loose fitting covers or batteries - quite the opposite in fact, I'd say it was a little too snug round there if anything (but that's what you want I guess!). Anyway, take a look at the photos I've linked to below and compare....
As for them being "all like that"... they aren't and if the box is not sealed, you have every right to claim that you not been sold a new product. Ask for a sealed replacement or (even better if you have been lied to) a refund and take your business to another retailer.