Cultural Considerations (I can't figure out how Part 2 got ahead of Part 1, but that's OK): I've explained this sultural phenomenon before, but it's important to rehearse it here in the context of visas.   In many cultures, it is considered proper to use your influence to help a friend.  By extension, it can be assumed that friends will come to you to ask for favors that might be within your reach but not within theirs.  One such favor is helping to get a visa.  I have a short, unsatisfactory answer you can use: "I'm sorry, I can't help."

In Western cultures, we are raised to believe in the Rule of Law, and that legal and civil decisions should be made on the merits of the case and not because of personal influnce or preference.  We have laws against insider trading and racketeering, and we look unkindly at influence peddling.  It will hurt your foreign friends, in many areas of the world, to hear that you are unable to help them get a visa.  They will take it as "unwilling", not "unable" and will consider you less of a friend. 

Some embassies have "back-channel" procedures by which embassy personnel can endorse/recommend the visa applications of people they know, whether to gain favor or to otherwise move toward government objectives.  No embassy employee will, in good faith, promote the visa application of someone they don't know well and personally.  It's bad for security, which reigns supreme at present.  it also doesn't look good when the person they endorse uses the visa for other than its legal purpose.