Bechoros 4:8

If a person is suspected of selling sabbatical year produce, one may not buy even combed flax from him but one may buy spun or woven flax.

Bechoros 4:9

If a person is suspected of selling terumah (which may only be eaten by kohanim) as regular, secular food, one may not purchase even water and salt from him; this is the opinion of Rabbi Yehuda. Rabbi Shimon says that only things that are obligated in tithes may not be purchased from him.