I have been burned three times.
1) Never buy from a guy that runs a shop. If it is good he will use it on a customers car.
2)Always check adjustment screws that was expensive lesson. Look for water damage, steel screws and aluminum housings dont like water.
3)Gently shake or rock the carbs for floats, this will let you know if it has a float not of the mounting tabs are broke. Back to lesson 1
4) Never ever buy carbs from Stan lives in Redding old man at Bugorama drag strip side close to the front of meet. He will trow 2 Webers together and claim they are matched. Back to lesson 1
If you buy them right it hurts less.
Now who wants to buy some Webers
The top two on the right have water damage and frozen adjustment screws. And about a $200.00 investment.