Buying FAILED DDR3/DDR4 RAM

How can I tell if the ram id DDR3 or 4? I looked it up on google and in the images some shows 3 or 4. But some ads state 3 or 4 but I do not see it on the stick. I only have maybe 75-100 sticks. I scrap computers when I get them. But mostly scrap wire, brass and copper.

You say you buy failed 3 & 4, but what if they are still good, what do you pay? Pricelist?

Go here for pricelist. https://www.ibuy.parts/home/ram ,He also buys processors, video cards, etc for better than scrap prices . I've done business with him a few times worked out great.
DDR3 and DDR4 looks different like most other different types of memory- the notch on the bottom of the ram where is presses into the slot is in a different location. The easiest way to tell outside of reading the label is to match it up the notch to one that is labeled DDR 3 or DDR4 ( most usually are ) .
Good luck .