Partial cover and concealment are identical to cover and concealment.
It's a confusing terminology change that happened part-way through 4e's lifespan, not the addition of an extra level of cover and concealment. The modifier "partial" was added to 'normal' concealment --probably in a well-meaning effort to clarify things-- and both the Rules Compendium and the Online Compendium parenthetically note that it is "sometimes simply called 'concealment.'" (RC 222)
The Online Compendium's glossary entry on cover still hasn't appended the modifier "partial," nor does it note that this word might sometimes be added, but the Rules Compendium uses the phrase "partial cover" and adds that it is "sometimes simply called 'cover.'" (RC 220)
Keep an eye on "superior" and "total," too.
There is equal potential for confusion in the upper echelons of cover and concealment: better cover is called "superior cover," while excellent concealment is "total concealment." I see no particular reason these two similar effects should have different modifying terms, and am surprised that only one item (the Nightmare's Keen Senses from DR 393) is currently confused by this (according to a search of the Online Compendium at the time of this post).
While both members of the shadow community, a fence and a fixer operate at different levels of it and have different roles.
A fence is a merchant dealing in black and grey market goods. They operate on the fringes of the shadow community - offering services to both members of the shadow community and the more garden-variety criminal. Depending on their specialization, they may even sell to normal people; in some environments, staples of life have to come in via less-than-legal channels. A fence can hook you up. They frequently but not always have corporate contacts, albeit unofficial. ("It fell off the back of a truck.")
In some cases a fixer operates as Mr. Johnson, in others he merely connects shadowrunners with one. No matter what, a fixer is embedded much more deeply in the shadow community. They deal in information, not merchandise, and that information is who's-who in the shadow community. A fixer knows the services an individual shadowrunner can provide, the kind of jobs they prefer to take, and the other runners in a local shadow community they can/will work with.
A significant difference is how shadowrunners interact with them. Generally, the shadowrunner approaches the fence. Unless you've made a whole lot of noise on a run, a fence isn't going to know what you've got to sell (or want to buy) until you tell him. By contrast, a fixer comes to you. The Johnson comes to him, and he reaches out to his network of shadowrunners to find the right team for the job.
The same person can operate as both a fixer and a fence. That's one person with two roles, it doesn't make the two roles into one.
Best Answer
In a traditional TTRPG table dynamic the Player Characters have the role of the protagonists in the story.
The Game Master/DM has the role of a narrator and facilitator who guides the players and PCs through the game. In order to do that they embody various Non Player Characters (NPCs).
A DMPC is a character that is controlled by the DM but instead of being supporting cast character to the protagonists (PCs) the DM positions them as a protagonist, the focus of the story.
A DMPC does not necessarily have to be a sign of bad DM practices, but it often is. Campaigns with DMPCs run into various issues: