Promoting Fiverr Gig Via Facebook Ad

Well I don't know if the TOS allows it, so someone else can answer to that.

But think about it from economic perspective.

With FB ads you usually pay $0,05–0,10 per click. Could be higher, could be a bit lower.
Fiverr gig will give you $4, right?

Let's say your Fiverr gig converts at whopping 10% (1 in ten visitors buy the gig). That means that each visitor is worth 4:10 => 40 cents. So theoratically if you pay less than 40 cents / clicks you should be good, right?

Well not quite. Your time costs something also.

Lets say you can do 5 gigs / day, so you make $20/day. You want to have $15 to your pocket after costs (advertising).

So now you can spend $5 / day to advertising. You'll get about 50–100 clicks for it, right?

Ok, so you need to make 5 sales / day for those 50–100 clicks. So your conversion rate will have to be at least that 10%.

Just tweak the numbers (click costs, conversions, etc) and you can see if it is profitable for you or not.

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Short answer: you probably cannot advertise Fiverr gigs on FB and do it profitable way