Don’t buy a pig in a poke.
More Dutch Proverbs:
If you eat someone's cake, you must also eat his lentils.Dutch
The first occasion offered quickly take, lest thou repine at what thou didst forsake.
Dutch
It is ill catching hares with drums.
Dutch
A fool may give a wise man counsel.
Dutch
Where poverty comes in at the door, loves flies out at the window.
Dutch
Precaution said, Good friend, this counsel keep: strip not yourself until you're laid to sleep.
Dutch