I'm a big fan of fiverr. Yes, you end up paying more than $5 for most gigs but if you need channel art, thumbnails, etc. it's a decent place to go.
The issue isn't wether or not one gig is legitimate or not. I've no doubt the guy offering to give you 200 likes will actually get your account 200 likes. So in one sense it's "legitimate". But what you're buying is not actually legitimate.
Imagine this. If someone on Fiverr said I'll sell you $10,000 in fake $100 bills for $5. Would you think it's a good idea? I mean the guys legit? He's got good reviews? He will actually give you $10,000 in fake money for $5? Not only that. Your neighbor got $10,000 in fake money from him for $5 and he says they actually arrived and it's looks pretty real?
Would you do that? Of course not, because although the guy will actually do what he said the entire concept is shady as hell. You'd go to jail.
You're essentially trying to do the same thing here. Yeah he might do it. But YouTube might ban your channel and you from ever doing business on YouTube. The likes won't help at all.
Just stay a mile clear of anything that seems shady like this.