I would agree with Murad. It depends on how smartly you work if you hire an SEO professional with years of experience he will know which sites have the domain authority related to the niche you are targeting and who to email or talk to in order to get those links. As well as knowing what quality content they are lacking on that platform. As well as knowing how to analyse keywords and tweaking pages ont he site in order to rank higher for certain terms.
However in comparison if you hire somebody who is less experience they may spend a lot of time generating no follow links which don’t have much of an impact and trying to compete on high competition keywords when it might be better to get 1st on Google with a low competition keyword.
To answer your question it depends on a large number of factors but the main ones are how competitive is the keyword you want to rank for, how high is the domain authority of the site you are trying to rank and how good is the person who is trying to improve the site.