If you could get a campaign working it would be an incredibly effective way of getting clients. All inbound leads plus the ability to turn on and off in an instant.
In basic theory it should work. Here's an example for web design
CPC of keywords in the web design niche = £3-4
Average conversion for campaign = 2%
Value of conversion = whatever you charge I.e. £250 setup fee+ £15/month hosting
100 clicks cost £350
2 conversions = 2 x 250 = £500 + £30/month recurring
More than enough to cover the cost of acquiring a customer and then some. Not even taking into account any upsells over the lifetime of the customer.
Obviously these figures are the subject of the discussion and I've just estimated these as closely as possible. Clearly there's not a lot of room for these figures to deviate and the campaign would need to be very well optimised.
So why does no one do this or does it actually work really well and is kept quiet...!?