As a player, I'v long disliked the idea of my character being subsumed into the service of some random nobleman or lord. In a true feudal society, everyone is in the service of someone else, and answers to someone. This doesn't mesh with the mentality of the average RPGer, who tends to see their characters as freelancers. In that regard, I decided to create an entire society based on the idea of freelancing, and free markets. Serfdom and slavery (are for the most part) out-moded, and modern (to our ears) ideas of property rights and freedom exist.
The only way to get stuck in service to someone is to sign a contract with them. Breaking the contract doesn't make you so much a criminal, as much as anathema to the business class. Of course, the individual you broke the contract with might choose to take some revenge, such as putting a bounty on your head.
Think of the average adventurer as a sort of Han Solo, and the average merchant as a kind of Jabba the Hut. There is no imperial law, but individual cities have laws, and there are guilds and trade unions to deal with.
Most of these merchants get the heebie jeebies when characters like Paladins or Rangers come around, as these are types that have their own motivations and generally can't be bought. Rangers generally couldn't care less about business deals between Merchants, but when they include dark inhuman forces, they tend to pay attention. Paladins are their own problem, but generally won't interfere with a contract between two parties unless it is grossly unfair to someone of little power, and even then they will try to "lawfully" equal the playing field.
There is plenty of room for hired swords in a wild west type format, as people generally aren't interested in getting into anyone else's business, and generally speaking, the elimination of an opponent tends to be advantageous. So unless it is their money or blood involved, they are likely to stand by as spectators as they watch opposing factions take each other out.
Most towns and villages have one petty little landlord type (a Mr. Potter), who is always looking to leverage his wealth to the disadvantage of those desperate enough to rely on him. Barnaby from March of the Wooden Soldiers is one of my favorite petty merchants.
Not to mention he later aligns himself with the Bogeymen. A perfect D&D villian!
Merchants should be the source of a lot of fun and role play in a campaign. They can be generous philanthropists, have secret political agendas, or just selfish sobs looking to make a buck. One thing they tend NOT to be is brave and loyal when things don't go their way. Have fun!