Learn French: Négocie le prix, puisque l'état est mauvais ! - Negotiate the price, since the condition is bad!

Puisque is used when the reason is already obvious, evident, or known to the person you are talking to. In this sentence, the bad condition of the item is a shared fact that both people can likely see. If you were giving a new, unknown reason, you would use parce que.

Why is it "négocie" and not "négocies", since it is an order to "tu"?

For regular verbs ending in -er like négocier, you must drop the final -s in the tu form of the imperative (command) mood. So it is Négocie ! rather than Négocies !.

Does "l'état" always mean "the state" as in a government?

No, l'état is very frequently used in everyday French to mean the physical "condition" of an object. Here, l'état est mauvais means the item you are buying is in poor condition.

Why does "puisque" not drop its final "e" before "l'état"?