Learn German: Da der Handel endet, sinkt der Gewinn. - Since trade is ending, the profit is falling.

Wegen is a preposition, so it must be followed by a noun phrase rather than a full clause containing a conjugated verb. You would have to change the action "since the trade ends" into a noun, such as "because of the end of trade" (das Handelsende). Applying the genitive case, the sentence becomes: Wegen des Handelsendes sinkt der Gewinn.

Could I use weil instead of da in this sentence?

Yes, weil and da are grammatically identical here—they are both subordinating conjunctions that send the conjugated verb (endet) to the end of the clause. However, da is often used when the reason is already known context or background information (much like "since" or "given that" in English), whereas weil is usually the direct answer to "why?".

Why does the second half of the sentence start with the verb sinkt instead of the subject der Gewinn?

This happens because of the "verb second" rule for German main clauses. The entire dependent clause (Da der Handel endet) occupies position one in the sentence. To keep the main verb in position two, sinkt must come immediately after the comma, which pushes its subject (der Gewinn) to the other side of the verb.

Does der Handel also mean a physical shop or a specific business deal?