The premixed rattlecans are normally Really Good. Ask them to look up your paint code on the system, 'cause some manufacturers will issue different batches of paint with sub numbers, to cover inconsistancies between batches.
e.g. Say your code was 123, the computer might list 123, 123/a, 123/b....
These are different batches of the same colour, which are slightly different shades. If this is the case, ask them to mix a small amount of each for you to test, (they SHOULD not charge for this). When you find the right sub code, get them to mix it up into cans, but be warned the mixed stuff is £10.99/can not the £5.49 you are used to.