Keep in mind that that $2 fee applies to any orders under $40. Above $40, the fee is only 5% of the total sale. Fiverr can charge whatever fees they want to on their own website. If those fees start driving customers away, they’ll change them. But I’d guess that the fees are not driving any significant level of legitimate customers away. $2 is not an unfair fee.
It would seem too, that Fiverr is encouraging buyers to place higher-value orders. A $2 fee on a $5 order does seem steep. But, then again, a $2 fee on a $35 order isn’t unreasonable. Fiverr wants to promote the idea that sellers offer higher-value services, and they clearly want to shed the cheap “everything is $5” reputation.