amazing??

Only the first one carries the meaning you want. To feel amazing is not the same as to feel amazed. Check a dictionary.

I suggest

Our chocolate cakes will amaze you.

Hello, chiaking—and welcome to English Forums.

Your native speaker is unreliable, and you were right at first. 'Amazed' is the feeling of the person experiencing it; 'amazing' is the experience itself. What may have confused your native speaker (if s/he was not already confused), is that we don't usually use that form at all; we use this:

Our chocolate cakes will amaze you!

Mister MicawberOur chocolate cakes will amaze you!
You will be amazed by our chocolate cakes!

Ah, yes, the exclamation mark is a good idea.

PS: There is a mnemonic that I teach my students, chiaking:

'-ing' is the thing, and '-ed' is me.

The circus was amazing; I was amazed
The race was tiring; I was tired.
etc

Thank you so much! Now I can sleep!

Thank you !!!! I was right!

chiakingI thought first one is correct because the customer will be amazed

Right.

chiakingnative speaker told methe second one is correct. why???

That speaker was confusing it with "Our chocolate cakes are amazing" ~ They can amaze you.

The cakes are amazing. Customers are amazed.

amazing cakes / amazed cu