I extensively use assorted major domain services such as Escrow.com, Afternic, Uniregistry, and Sedo. They provide important sales services, often without up-front costs. You typically need pay them only when your product is sold. Their costs are not unreasonable, and their published services are dependable. I am happy with them generally.
There are a few problems however.
Some of these services deliberately keep buyer & seller apart, and maintain a measure of secrecy.
They promote fixed prices, Buy-it-Now (BIN), which can be difficult or impossible to edit quickly.
A possible big problem is that they have insider access to your unpublished data & information as well as that of others throughout the industry. And their employees (or the services themselves) can take advantage of their insider market position. Might they directly buy your under-priced domain?
This is most perverse when one or more newly-made big sales leaves your domain or portfolio suddenly under-priced. Others can act before you hear anything.
These markets are largely unregulated -- Watch out for yourself!
