uuallan,
Some domain business sell their service for many reason, can be financial, technical and other related issues.
I've seen some folks here selling domain name registration services, though I noticed that they are not active member of this forum. They just created a reseller account then selling it for high price. Just like retailing type of business as they say in real estate business, buy low and sell high.
Just in case you were able to see domain name services for sale with active customer, let's assume a couple of hundreds active registration. Are you willing to pay the price and what range? This is the common question of domain investors. I'm telling you they are not cheap.
If you are planning to start-up a domain name business you have to plan for it, catchy business name and domain name, advertisement play big role, active support, etc.. I guess this is a cost effective approach, long term program and you will be able to establish value to your business.
Visit this link to see other domain name business active today:
http://www.needguide.com/live/modules.php?op=modload&name=Web_Links&file=index&req=viewlink&cid=42
Not a complete list though but will start you somehow.
I'd like to take this opportunity to invite other domain name businesses to list their site here.
http://www.needguide.com/live/modules.php?op=modload&name=Web_Links&file=index&req=viewlink&cid=42
Keep in touch if you need assistance,
tw.