Actually it's not good if your friend brings on a friend that doesn't get along with your group of friends.

But yes, when money is involved, you have to be careful because there's a thin line between being fair/friendly and taking advantage of you.

will allways be a problem when it comes to money.
but its a nice way to be helpfull while getting better at whatever you do.

i've done biz with friends, no prob. it's actually good because you'r building on an existing base.

problematic...when it comes to pay

Never!
If you want to keep your friends as friends avoid doing business with them.

Sometimes too many people think they are real friends with me, A few weeks back I did an album design for "friends" and soon they have their release party, but some days back he said to me that I maybe wont get in for free, because their guest performances also get in for free, and they are more important.

But without me they wouldnt even had their album done, i worked so long on the album, and then they started bitching.. but Now i get the album and I get in for free! But they know that I won't do it for cheap next time.

friends try to take advantage of your skills while being oblivious to the fact that you deserve a reasonable compensation.

Depends on the situation but, generally avoid business with friends. If you're working together, a new level of diplomacy has to be exerted if one is not holding their own. If they're coming to you to design stuff, they might expect a discount. It can work sometimes ... sometimes.

Mixing financial interest and frienship didn't work in the past. It kinda brings out the worst in people...

Working for friends for small favors is alright, but working with them.... yeah don't do it.