Learn German: Haben Sie etwa den Verdacht, dass ich stehle? - Do you seriously have the suspicion that I am stealing?

In this context, the modal particle etwa adds a strong tone of disbelief, shock, or indignation. Without it, Haben Sie den Verdacht, dass ich stehle? is a completely neutral, factual question ("Do you have the suspicion that I am stealing?"). Adding etwa makes the question defensive, translating roughly to "Are you seriously suspecting..." or "Do you actually think..."

Doesn't etwa usually mean "approximately"?

Yes, but only when used as an adverb with amounts or numbers (like etwa zehn Euro for "about ten euros"). Here, it functions as a modal particle. Modal particles don't have a direct dictionary translation; instead, they change the emotional flavor of the sentence. In questions, etwa signals a negative expectation or unpleasant surprise.

Could I use the verb verdächtigen instead of the noun phrase den Verdacht haben?

Yes! You could say Verdächtigen Sie mich etwa des Diebstahls? (Do you suspect me of theft?). However, den Verdacht haben, dass... is a very natural and common way to express this, especially when you want to follow it with a descriptive dass (that) clause. Note that if you use the verb verdächtigen, it requires an accusative object for the person and a genitive object for the crime.

Since a suspicion is not a confirmed fact, shouldn't stehle be in the subjunctive mood?