E.g. Tim Horton's choice messed up by important customer having left (15)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Anagram (messed up) of CHOICE , then KEY (important) + PAYER (someone who pays = customer) around L (abbreviation for left). I had to ask Wikipedia about Tim Horton ; can’t say I know much about the sport.