What should be done with Sta”m that is in the possession of a non-Jew?

There is an obligation to purchase any Sta”m which is in the possession of a non-Jew. If such items remain in his possession, they may become desecrated. If the non-Jew is demanding an exorbitant price, the Jewish buyer should negotiate to pay only market value. If the non-Jew is insistent, the items should not be purchased. Otherwise, an incentive would be created to seize such items and demand hefty prices for them.

Who can be trusted on matters of issur v’heter?

There is a rule that a single witness is trusted regarding issues of issur v’heter (forbidden and permissible matters). According to Shulchon Aruch, any person can be trusted in these matters as long as he does not have a history of causing others to sin. Rema maintains that he must have a chezkas kashrus (i.e. he must be established as a person who follows the Torah). Some poskim say that if he wears tallis and tefillin daily, davens three times a day, washes his hands before eating and runs his home according to halacha, he has a chezkas kashrus.

Is there a reason to check tefillin?

Tefillin which were made properly and are worn daily do not have to be checked for kashrus. If something happened which calls the kashrus of the tefillin into question, however, they must be checked (e.g. if they developed a rip or if they were left in a moist area). In such cases, the brocha for wearing them may not be said until they are checked. The earlier poskim say that even though one is not obligated to check tefillin which are worn daily, doing so is recommended out of concern that perspiration could affect the tefillin. Contemporary poskim say that since tefillin today are made from superior materials, this concern no longer applies. Furthermore, opening the tefillin for checking may end up causing other problems.