I am a new believer and struggling to find a good church. Many of the churches close to me are big enough to have gift shops inside! Isn't this wrong? Selling next to where they are preaching doesn't seem right to me. Didn't Jesus say not to turn his father's house into a market?
Jesus' comment regarding selling in the temple of God was made in a specific context:
Mark 11:15 Then they came to Jerusalem. And He entered the temple and began to drive out those who were buying and selling in the temple, and overturned the tables of the money changers and the seats of those who were selling doves;
Mark 11:16 and He would not permit anyone to carry merchandise through the temple.
Mark 11:17 And He began to teach and say to them, “Is it not written, ‘MY HOUSE SHALL BE CALLED A HOUSE OF PRAYER FOR ALL THE NATIONS’? But you have made it a ROBBERS’ DEN.”
Jesus' disgust at the activities in the temple reflect the specific nature of the temple and of these offenses. The temple was intended as a meeting place for God and men, but over the centuries the Pharisees turned it into a place of commerce. The danger in this practice was in diminishing the importance of God and the purpose of the temple.
In our day, the temple of God is the physical body of the believer:
1Cor. 3:16 Do you not know that you are a temple of God and that the Spirit of God dwells in you?
1Cor. 3:17 If any man destroys the temple of God, God will destroy him, for the temple of God is holy, and that is what you are.
So the direct application of Jesus' concerns in Mark 11 would be that we work to purify our body from unholy behavior. This is our spiritual service of worship Paul says:
Rom. 12:1 Therefore I urge you, brethren, by the mercies of God, to present your bodies a living and holy sacrifice, acceptable to God, which is your spiritual service of worship.
Rom. 12:2 And do not be conformed to this world, but be transformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect.
Therefore, the church building we attend is not the temple of God. It's just a building, and as such it has no significance on its own. So we cannot take Jesus' words regarding the Jewish temple and apply them to a different kind of building, in this case a church.
Nevertheless, the New Testament does give rules for how the assembly of God's people should take place in any space:
1Cor. 11:18 For, in the first place, when you come together as a church, I hear that divisions exist among you; and in part I believe it.
1Cor. 11:19 For there must also be factions among you, so that those who are approved may become evident among you.
1Cor. 11:20 Therefore when you meet together, it is not to eat the Lord’s Supper,
1Cor. 11:21 for in your eating each one takes his own supper first; and one is hungry and another is drunk.
1Cor. 11:22 What! Do you not have houses in which to eat and drink? Or do you despise the church of God and shame those who have nothing? What shall I say to you? Shall I praise you? In this I will not praise you.
1Cor. 14:26 What is the outcome then, brethren? When you assemble, each one has a psalm, has a teaching, has a revelation, has a tongue, has an interpretation. Let all things be done for edification.
1Cor. 14:27 If anyone speaks in a tongue, it should be by two or at the most three, and each in turn, and one must interpret;
1Cor. 14:28 but if there is no interpreter, he must keep silent in the church; and let him speak to himself and to God.
1Cor. 14:29 Let two or three prophets speak, and let the others pass judgment.
1Cor. 14:30 But if a revelation is made to another who is seated, the first one must keep silent.
1Cor. 14:31 For you can all prophesy one by one, so that all may learn and all may be exhorted;
1Cor. 14:32 and the spirits of prophets are subject to prophets;
1Cor. 14:33 for God is not a God of confusion but of peace, as in all the churches of the saints.
Paul admonished the church in Corinth to meet in an orderly, loving fashion without resorting to selfish debauchery. Therefore, anything done in the context of the gathering which detracts from order and godliness would be wrong. Is selling books in the church building contrary to these requirements? Not necessarily, and in the end that would be a judgment call for the elders to make.