While SteemIT is mostly a content and social platform, I hope we can encompass a lot more tools and/or services internally providing layers of extra functionality that will be useful to users.
This post will explain how the Repholder's Manual Escrow Service (BETA) for a marketplace or simple escrow will work, until an automated one is built by someone more knowledgable in terms of the STEEM API.
This is more about brainstorming than making profit, so the service will be provided for free with a max cap of 40 SD or 10 STEEM.
Step by Step Guide
1. Create a post in the marketplace and/or escrow tags with a WTB (want to buy) / WTS (want to sell) as the start of your posts title.
Example : WTS Logos For Businesses
2. Provide the relevant details - price, delivery details (if applicable), refunds etc etc with a link to this post.
Example:
Type : Digital Item
Item: Business Logo with 4 resolutions in both - jpeg and png format
Cost : 8 SD or 2 STEEM
3. The buyer/seller will comment on the WTB or WTS post
4. The initial poster will accept the offer
5. The amount will be sent to 
6. The person that accepted the marketplace/escrow thread offering will comment here stating he has received the goods/service.
7. I will send the relevant amount to original posters SteemIT account
As insurance I will be providing any proceeds (up to a maximum of 300SD) of this post to a trusted STEEM member, witness or the developers themselves.
You can also find me on slack most of the day 
Note: Hopefully we get this as a automated decentralized solution in the near future!!!!