This has been an interesting thread because it's from the Seller's point of view. I really think some Seller's are just not competent and over-promise which causes a lot of cancelled orders.
I use Fiverr a lot for AMR blasts, backlinking, and having some slick videos made for cheap. I have never had to cancel an order myself but I had two Sellers cancel orders because they could not deliver on promises.
I ask a lot of questions before buying a gig now to make sure the Seller really can deliver on what they promise BEFORE I buy the gig. I look at comments/ratings. There are Sellers who inflate the good comments by using multiple comments and they don't even try to hide it. Stupid!
This method has worked well for me because I have found a couple of Sellers I now go to for repeat work. For me, it's outsourcing the jobs I won't do or can't do myself. It's a win-win.
There are lots of crummy Sellers as well as Buyers on Fiverr. Both sides need to use caution. In the end, a good Seller can get a nice client list for repeat business and an honest Buyer can find someone they can trust for more work.
It's true that $4 profit per job does not seem much money. But, remember, in some parts of the world the Seller would not be able to make as much money for similar work. Of course, if they belonged to BHW, they could learn how to make much more than that and would not need to sell themselves on Fiverr.
Money makes the world go-round and for some Fiverr OP's it makes their world much nicer.