Surely the concern should be much more about stopping this person selling puppies at all! Not KC registered, no health checks, selling multiple breeds etc. I honestly think that you are completely wasting your time worrying that you may have been sold a working/show cocker!
You have not bought a crossbreed at all, it cannot be compared to a cockerpoo as it is not 2 different breeds, it is the same breed with a different purpose!
If you have paid more than £300 for a non KC registered, not health checked cocker spaniel you have been had anyway! It would be irrelevant whether that was for a show or working cocker.
I am sorry, but I think you did not research the background of your puppy well enough before you purchased it and it is too late to try to compensate for that now. Please just enjoy him for what he is.