If the knife flipped fine when you got it and then got worse after you continued to flip it, I don’t think the seller sold it to you knowing the washers were bad. I’m speaking from experience, because I had the same issue with my Southard. It flipped fine at first and within a short time began to degrade.
Also, I sent my knife to Spyderco and they claimed it had been disassembled, even thought i bought it new from an authorized dealer and never disassembled it (I knew better not to).
In the end, you got a great knife at a great price. Enjoy.