Learn Turkish: Fiyatı çok yüksek bulduğunuz için pazarlık yapıyorsunuz, değil mi? - You are haggling because you find the price very high, aren't you?

In Turkish, değil mi? usually acts as a fixed, invariable tag meaning "isn't that so?" or "right?". Even though the main verb yapıyorsunuz is in the formal/plural "you" form, you don't need to conjugate the tag to match it. Just adding the standard değil mi? to the end of the sentence works perfectly for asking "aren't you?".

How does bulduğunuz için mean "because you find"?

To say "because someone does something", Turkish uses the -dık participle plus a possessive ending, followed by için. Here, bul (find) + duğ (the softened form of the -dık ending) + unuz (your) + için literally translates to "for your finding".

Does bulmak mean "to find" in the sense of having an opinion, just like in English?

Yes! Just as in English, the verb bulmak means both to physically find a lost object and to hold an opinion about something (like finding a price high or finding a movie boring).

Why does fiyat (price) have an -ı at the end?

The -ı is the accusative case marker. It shows that fiyatı is the specific direct object of the verb bulduğunuz (you find). You are finding "the specific price" very high, so it requires the accusative ending.