> Buy goods/services from your friends
I actually don't think that's a good idea. I have observed so many friendships break this way that I think it is not worth it. I also have bad experiences personally.
Why would you want buy/sell services with your friends? To get a better deal? If you are getting a better deal out of this, you are likely to cause your friend to think they are getting bad deal and are exploited in this relationship. If you don't want to get a better deal than the market rate, just go and buy from anybody else in the market.
Even if you buy/sell with the friend at a market rate, he or you might be pressed into thinking you or them are expected to provide a better service. And this might come with the resentment ("I am being paid the same but expected to do more/better job")
If you provide services at a market rate to a friend, they might think they should be getting a better deal from you for the fact you are their friend. So for example, if you are a car mechanic and you are fixing their car, you might be doing a more thorough job but still charging them the same and at the same time they might not be able to appreciate that they are already getting a good deal and be unhappy with what they are getting.
As I work with computers / do software development, I simply refuse when friends ask me if I can do a website for them or fix their computer. I certainly could do this, but I am also certain that nobody is going to be happy with this relationship. My real hourly rate is so enormous and my website making skills so poor that they are 100x better just going to fiverr which is what I try to steer them to.
So my personal rule is to try to stay away from doing business with my friends unless they are friends that became my friends because I was doing business with them in the first place and we have healthy business relationship. I call them business friends/acquaintances. These people actually understand the business and understand the services I provide and can appreciate when they are getting a good service. I can charge them more than market rate and they will still be happy because they are getting much better service with much less risk.