i like all the idea of how useful steemit can be. the idea of using it to promote services is most likely the best one. everywhere else they will take money from you to promote your service and in steemit you will get paid for your post.
but i am not so sure about what you said about replacing fiverr. unless you know someone really well or have a good relationship with them you can't trust them to do their work.....
There is the #steemgigs community. People make posts about their services and when you hire them you can pay them in Steem. There is exactly the same amount of trust as with Fiverr. If you want to make sure you can make a contest first and give some money for part of the work and hire the winner. That way you know it will be good.