We might be good, but even we can’t argue that a motorcycle wasn’t fit for its purpose because it didn’t match your helmet, or that you should have a refund because you underestimated your beer gut on buying a new race suit and you couldn’t do the zip when you got home.*
Where the problem has arisen as a result of your mistake or the fact you have changed your mind, refunds or replacements are purely up to the goodwill of your particular dealer, and they are entitled (given that they don’t have to do anything) to offer you a credit note instead or simply to say no.
* note, however, that if you were fitted for your helmet before you bought it and you subsequently find you were given the wrong size, or your leathers were tailor-made and they wouldn’t fit your little finger, you may have a claim.