Responsa for Bava Batra 14:9

Q. Leah claims that she settled in the town T subsequent to the demand of a tax from the Jews by the burghers of the town, and after they had instructed the Jews to pay the tax to a Jew, A; that she was, therefore, not subject to this tax, even though A gave the community an extension of the time for payment; and that the community had no right to collect any money from her in payment therefor. The community claims that Leah sent her money to T for investment before the burghers demanded the tax; that her sister rented a house for her, which indicates that Leah had decided to reside in T before she actually came there; that it is a custom of the community to collect taxes from all those resident at the time of collection even though they were not residents at the time the tax was demanded; and that the tax was paid in order to save their lives, since the burghers threatened "to do what they did on the Rhine." Leah denied the claims that she sent her money to T, that it had been invested before her arrival and that her sister had rented a house for her. She stated that the Jews always paid a tax to the burghers whenever the latter demanded it; and that she did not intend to settle in T at all, but that being her sister's surety she had to follow her sister when the latter fled from her former settlement.
A. Matters of taxation depend on local custom. It is needless to ask me the custom of our community, for you may have a different custom. Anyone who settles in a new place is bound by the custom prevailing there. But since the community has completely settled its obligations to the burghers, by consenting to pay the tax to A, before Leah settled in T, the representatives of the community must prove through witnesses who are not residents of T, that according to their custom Leah was obliged to pay the amount the community demanded, before they could deprive her of any of her property. If Leah, however, rented a house in T before the tax was levied, she is bound to pay her share of the tax, despite the fact that the community may not be able to prove any prevailing custom to that effect.
SOURCES: Pr. 995. Cf. Menahem of Merseburg, Nimmukim (8).