To answer these questions we first need to have a little background about what the people in the temple were actually doing. The most detailed account of this Bible story comes from John 2:14-16:
14 In the temple courts he found men selling cattle, sheep and doves, and others sitting at tables exchanging money. 15 So he made a whip out of cords, and drove all from the temple area, both sheep and cattle; he scattered the coins of the money changers and overturned their tables. 16 To those who sold doves he said, "Get these out of here! How dare you turn my Father's house into a market!"
In the other passages of the Bible where this account is told (Matthew 21:12-13, Mark 11:15-17 and Luke 19:45-46), Jesus accused the merchants of turning the temple into a "den of robbers". This phrase is referring to Jeremiah 7:9-11 where Jeremiah shares with the people of Judah what God had shown him. He is saying that those who were doing wrong went to the temple because they thought that, just by being in the temple, they were safe in doing their detestable things. Thus, because the temple that Jesus evacuated was crowded with those who were doing wrong, He called it a "den of robbers".
Jesus called those who were selling in the church a "den of robbers" because the people exchanging money and selling animals in the temple were actually ripping the people off. There were two ways in which these merchants were ripping the people off: 1) they were charging more to change the money and 2) they were charging more when selling the animals used for sacrifices.
During that time, there were a lot of different coins in circulation. During Passover, the temple would charge a temple tax but they would only accept Jewish coins. The difference between the Jewish coins and other coins in circulation was that the Jewish coins had images on them that were not objectionable because they did not violate the command against graven images, but some of the other coins had images of pagan Gods.
Because the Jewish coins were only accepted, temples had money changers who would exchange the unacceptable money for the Jewish money. The problem was that the money changers in the temple that Jesus evacuated were charging extra for their services.
Not only were the money changers charging too much, but the merchants selling animals used for sacrifices were as well. There were many occasions when Jews would be called upon to offer an animal sacrifice at a Temple far away from their home. It was not practical to bring their animals with them on such long trips, so they would buy the animals at the temple for sacrifice. The problem came about when the merchants would charge more money than they should have for the animals. As you can see, Jesus was not upset that there were merchants in the temple selling things, He was upset because the merchants were ripping His people off.
At Fellowship Church, we have a bookstore and a coffee shop called "The Source". The Source is a ministry that Fellowship uses in order to provide for those who are seeking, and to help believers grow in their walk with Christ. The cafe is a place where people come together to build relationships throughout the congregation, have meetings, and enjoy a serine place to indulge in God's word. How can something that brings so many people together and attracts so many non-believers be wrong? When it comes to selling things at church, I believe that as long as what you are selling is used to further God's kingdom, God is all for it.