Is zakat obligatory upon a merchant who owns a shop and capital, but suffers from increasing financial deficit that prevents him from covering his expenses, and what is the ruling on evading unjust taxes imposed by the state?

Zakat (definition) must be paid on the remaining trade money if it reaches the nisab (definition) and a full year has passed over it, as Allah Almighty says: ﴿Take, [O, Muhammad], from their wealth a charity by which you purify them and cause them increase﴾ (Quran 9:103). There is no sin in resorting to stratagems to avoid oppressive taxes imposed by the state.