What does the Bible say about selling in the church as a way of financially supporting the church? I know that some churches allow selling to take place.
The only mention in the New Testament of any means for churches to get money is through free-will contributions by members.
“Now concerning the collection for the saints, as I have given order to the churches of Galatia, even so do ye. Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come. And when I come, whomsoever ye shall approve by your letters, them will I send to bring your liberality unto Jerusalem. And if it be meet that I go also, they shall go with me.” (1 Corinthians 16:1-4)
“Every man according as he purposeth in his heart, so let him give; not grudgingly, or of necessity: for God loveth a cheerful giver.” (2 Corinthians 9:7)
Although both of these, as well as some other passages about individuals giving directly to those in need, are about contributions for specific needs, they do set a pattern for giving in the church. The passage in 1 Corinthians 16 specifically mentions a treasury (“in store”).
The question here becomes similar to the question about instrumental music. Basically it comes down to whether the silence of the scriptures bears any weight. Since there are specific scriptures about giving, but none about selling anything or playing bingo or other methods of raising funds, the more conservative interpreters would say that those other things are excluded. Those of a more liberal mind would argue that free-will contributions are one method of raising money, but that there is nothing in the scripture that would specifically forbid casino nights, garage sales, or selling t-shirts or chorus albums. Nor would it prevent a congregation who took the latter interpretation from owning grocery stores, bars, casinos, department or specialty stores, or any other type of business short of prostitution. I even read about a church that operates a theme park in Florida as a means of supporting its outreach programs.
Of course, in the United States, when a church gets into the business of selling something they must fight with the government about whether doing so will take away their tax exemption. Operating a business could result in the church having to pay taxes on all their income, including free-will contributions.