Wow quick answers you guys!!!
Thanks all
I think i made the right decision not to buy him (although he was soo cute!!) I have read up online and it says that if it is a common they will grow up to 18" How can a shop sell fish when they have no clue what it is, it wasnt even a shop boy it was the shop owner who had no clue!!! no wonder people end up with huge fish they can not house (makes me mad)

i do already own 1 common not albino he is in the 3ft goldfish tank (he was in with goldfish when i bought him)
he was about 2" when i got him and now approx 6" but i have had him for 6 years.