Learn Swedish: Kunden klagar eftersom maten är dålig. - The customer complains because the food is bad.

Yes! Both eftersom and därför att act as subordinating conjunctions meaning because. In Swedish, eftersom is often used when the reason is already known or less emphasized, similar to the word since in English. därför att puts more focus on the why. In this sentence, you can use either one perfectly fine.

What happens to the word order if I start the sentence with Eftersom maten är dålig?

If you put the eftersom clause first, you must remember the verb-second (V2) rule for the main clause. The entire first clause counts as position one, so the main verb klagar must come immediately after it: Eftersom maten är dålig klagar kunden.

Why are we using the definite forms kunden and maten here?

Just like in English, we use the definite forms when talking about a specific situation rather than customers or food in general. Both kund and mat are en-words, so they take the -en suffix to mean the customer and the food.

Why is the adjective dålig instead of dåligt?