Guidance on handing a private plugin request?
How do we go about if I request a plugin from a developer I have the following questions,

How do we do the exchange to ensure both our interests are met?
How do I make sure I receive what I'm paying for?
How do I know I'm not getting overcharged?
How do I transfer the money to the developer safely?
After I received the mod am I the solo owner and have stand-alone rights to it?
How do I ensure the developer doesn't publish it for free on uMods?

Any advice will be appreciated

Thank you 

Usually people just ask experienced and trusted developers and do not care. To know if you are not getting overcharged, just ask other developers if the price of N plugin from Y developer is ok. Because some developers can make bad code and charge 10$ for example or good code and charge 100$ for example, so in first case you can get bugs and problems and in the second one I guess you won't if you selected a good developer :p

In response to RobStilSkin ():
How do we go about if I request a plugin from a developer I have the following questions,

Currently noone can provide you with 100% guarantee on these questions. Most of the devs care for their reputation, so they probably won't scam you, but it depends on many factors. You should make a clear request with all the following questions answered - Full plugin description, with all the functions specified BEFORE dev names you the price, because if u want a plugin with 2 options, and dev charges you with 10 bucks, and starts the job. Then you ask him to add 20 more functions, but u dont want to raise the price, thats not appreciated. 
Personal releases (plugins that dev cannot resell/give to someone else but you) must be also discussed before naming the price, because they are always more expencive, since dev cannot receive additional money from other clients. 
As I and Misticos said before -> reputation is the key, ask trusted developers, make them provide you with their previous work (free plugins here or somewhere else), so u can find out, how good they are.
Original Poster
Thank you, helps a lot and I do understand some questions are difficult to answer but just wanted to get the idea what was the normal process and how people are currently approaching this exchange of the code and cash.

With my client i do the following - we discuss the questions above, I do the job, drop a video demo, receive the money through PayPal or other system, and give the access to plugin.