(English) This is an essay. It expresses the opinions and ideas of some Wikimedians but may not have wide support. This is not policy on Meta, but it may be a policy or guideline on other Wikimedia projects. Feel free to update this page as needed, or use the discussion page to propose major changes.
1. Never make business that goes against the WMF mission statement
Best would be to do business when it actually helps our mission, but business is sometimes only a mean to bring in money. In any cases, no business deal should ever prevent us to go on our path toward "free access to knowledge to all, in many different languages".
Any time a business deal is proposed, read again the mission statement (http://wikimediafoundation.org/wiki/Mission_statement) and wonder if any detail of the deal might not be against our mission. Make the mission statement your bible. Read it and read it again.
Hint: exclusivivity, which prevent us to spread knowledge thanks to other parties, should usually be a deal-breaker.
2. Avoid making business with those who are not sympathetic to our mission and to our core values
Within our core values is freedom. The freedom to read, the freedom to use, the freedom to participate, the freedom to share. In short, we love transparency, we love non-proprietary software, we love openness. Any business deal that would tend to support the opposite should be considered with caution. Any time a deal involves using a proprietary software, ask yourself if a free-software might not be available. Whilst not deal-breaker, explore other options.
Hint: If the third party is trying to convince you that our core values are wrong, amoral or plain stupid, ask yourself why you are still talking to that person. To make her change her mind ? Good. To get sure you'll make the deal anyway ? Warning, you might be on the wrong path.
3. Avoid making business with those whose reputation will hurt ours
Remember, we are a non-profit charity. Whilst we need to money brought by business, our final goal is NOT to make money, it is to act for the common good. We enjoy a lot of trust and goodwill in the public, preserve that trust. Nurture good will. This is our best asset. If that means we should be poor, let's be poor. Better poor but appreciated, than rich with a lost reputation.
If a deal looks very juicy, be suspicious. Most business are not charities, their primary goal is to get richer. If they offer a lot of money, remember to ask yourself "what benefit do they get in the deal ?" immediately before asking yourself "might our reputation be damaged in associating ourselves with this corporation ?".
4. Beware the Internet bubble, do not get paid in Second Life money
Money is money. Stock options are stock options. Stock options turn to be money in most stable corporations. Stock options are paperware in many internet companies. Whilst companies will be happy to pay you in stock options for tax reasons, beware of the reality of the gift. Do not sell your soul for peanuts in hope of golden nuggets. Be realistic.
Hint: do not agree to sell domain names you do not own against buying stock of unknown value.
5. Remember many do not support advertisement, think twice before signing an advertisement deal
Some editors support advertisement, others don't. There are also many types of advertisement, from the bold one on all articles, to the softer one, on the search page only. Still, boldly choosing to put advertisement can get you a deadly feedback
Hint: go read the discussion about Answers.com tool back two years ago.
Second hint: go read the logo of matching donor discussion from last january