I have been both a buyer and a seller on Fiver and I've been disappointed both directions. As a buyer I've had sellers who delivered just horrible quality then got mad when asked to make it right. One even filed a complaint against me when the product he delivered wasn't even close to what he'd promised and I refused to pay. Another did such a low quality job that I think my kid could have done better. I understand I won't get much for $5 but in my case I offered more in exchange for better quality and the quality was still low.
As a seller I find there are very few orders and the site is a bit hard to navigate. Just try to find your own "gig" for example, even from your admin pages, to do edits.
My customers have liked my products and I've gotten "tips" on sales which in many cases doubles my income. The problem is the fees charged eat it up. Let's say I have a $5 item and I get a $5 tip so I made $10 from the sale. But then Fiver charges me $2 in their fees plus an additional $1 to send me my money via PayPal. If I want it sent any other way the fees are higher, in some cases MUCH higher. So Fiver is taking 30% of my gross income on the sale!
If I'd made the $5 sale and NOT gotten a tip they would have taken $3 of the $5 I was paid. Making $2 for an item isn't profitable.
In the "Price-Quality-Service, Pick any two" equation you're getting a very low price, but I'm just not seeing that you're getting either of the other two. When you only get one of the three items it's a bad deal and should be avoided. That's my advice for both buyers and sellers... Avoid it.