When we were looking for ours (A working one) we found there to be quite a mix of them out there.
I think it’s been said earlier up but if you get one with almost solid FTCH’s in the parent line odds are it’ll be a machine. This article, although it can seem negative, gives a strong opinion on working cockers and cockers from strong ftch lines.
http://www.felsteadgundogs.com/workingvstriallingspaniel.html
I’d suggest going along to a game fair, or such like, where there will be loads of them either on demos or with owners. Most if not all will happily talk to you about them, (Spaniel people are great!) the lines they’re from and what they’re like day to day.