Starter or just a bad key

[Britrover]

Hi,

Off late my 98 Boxster is beginning to have intermittent starting issues. Had the battery checked and it is good which leads me to the next possible culprit. On my 10+ year old Mercedes had a similar issue, and the dealer recommended changing the key which fixed the issue. Not sure if the same logic would apply to the Posrche. How do I determine if it is the key vs. the starter? Appreciate any input to get this issue sorted.