General rules on paying agents

I've found a couple of different real estate agents that are helping me, in various capacities, to find properties, and I just want to clarify my understanding of whats "typical" practices as far as payments from an investor to an agent...

I've gone through all the rock bottom blueprint materials and these are my questions based on the info as I understood it..

For the following purchase scenarios, what is best practice for investors paying fees to agents (both in effort to pay them accordingly for their time spent + build long term relationship)

- MLS Listing - they would just receive their % of the sales commission, which would come straight from buyer.

- FSBO Listing - if agents were involved in making offers, doing walkthroughs, etc.. Is there a ballpark $ amt you would pay typically? % of sales price? Whats the best practice?

- REO's - same question as FSBOs. Do you pay agents for these type sales since there isn't a set sales commission setup for agents.. How does this work in actual practice?

I just want to make sure that I'm absolutely fair with my agents, and that they feel valued (monetarily) for the work that they're doing for me, and just trying to get to the best practices that everyone's using in the real world..

In reality, I will be doing the majority of analysis, offer making, etc for the near term, so I want to be fair to my agents, but at the same time, if they've spent 0 time on the deal, I may not feel its fair for them to get a portion of my profit as a commission on a specific deal they haven't been involved in...

Hope that makes sense...

I really appreciate your help... Thanks,

Mark