One may not perform matters of accounting in a Shul. [Thus, one may not perform accountings of budget, salary, or payments in a Shul. Likewise, one may not sell items in a Shul.]
May one perform community related accountings in a Shul?
No. This applies even if the community does not have another area to gather.
May one sell items in a Shul?
May one sell Sefarim and other Tashmishei Kedusha in a Shul?
May one sell Chameitz in a Shul?
May one exchange money in a Shul?
May a Din Torah be performed in a Shul?
Seemingly it is permitted to do so being that it involves a Mitzvah.
 Michaber 151/1; Megillah 29b
 Michaber ibid
 Chesed Lealafim 151/3; Ben Ish Chaiy Vayikra 4
 Biur Halacha 151 “Vein Michashvin” in name of Ramban
 Piskeiy Teshuvos 151/10
 Rav Poalim 24; Ketzos Hashulchan 29 footnote 2
 Ketzos Hashulchan 29 footnote 2
 Piskeiy Teshuvos 151/10 in name of Mishnas Yosef
 See Rama 54/1; Ketzos Hashulchan 29 footnote 2