does failure in skill affect gig ranking?
There is no such thing as “gig ranking”. That being said, in general, if you do not know how to do something, and you have no skills in the service you are trying to offer, then yes, you will be hurting your ability to be successful as a skilled freelancer.
Offer services in the skills you possess. That is, after all, the entire purpose of this site.
Yes it certainly does. Your clients won’t be happy and you won’t be successful probably.
Eventually fiverr staff does take a look at most gigs and how they perform and skill is the top indicator.