How accurate is the apple store repair estimation?

Hi there,

I recently sent my macbook pro 13" in for repair.
They said they found some dried sticky substance on the battery.
I dont' know how it gets there.
After their estimation, they said they need to replace to whole main logic board.
Since I still have my appleCare and they need to order the part in, they gave me this estimated price of $750. (which for now is covered by the appleCare.)
But I wonder if they will change their mind last minute and decide to charge me that money.
Because the last sentence on the paper said "If liquid damage is found, contact customer for re-quote as water damage isn't covered under the warranty."
I wonder how many people may know about this situation.
Thanks in advanced.

Apple

If they determine that there's liquid damage (and thus the applecare is null and void on that repair), they will contact you BEFORE the proceed.