1."If you wanted my advice, I would think twice about buying a car like this."
2."If you want my advice, I will think twice about buying a car like this."
I think "If you wanted my advice" has the same meaning as "If I were you" so maybe the first sentence is correct.
I also would like you to give me your opinions about the second one.
Could you please explain why the sentence must be like that?
For the beginning of the sentence, "If you want my advice..." sounds better, because if this is spoken, we can assume that the person thinking about buying the car is listening. Between the first and second clause is an implied "If I were you".
I can see why you are confused, because we often use the past tense in such sentences:
"If you gave me a dollar, I would spend it". "If you give me a dollar, I will spend it".
But this is a little different.
"If you want my advice... " is similar to "If you ask me...", "If you want my opinion...", "If you're asking for my advice..." All these use the present tense.
"If you want my advice, [if I were you] I would think twice ..."
Thank you, Raymott, very much.
I am glad that you understand why I confused and explained it very clearly.
Thanks a lot.