In The Good, the Bad and the Ugly, Blondie and Tuco meet when Tuco is saved from three bounty hunters/bandits by Blondie.
Tuco is then worth 2000 dollars, and Blondie gets 1000 from their first scam and all three thousand from the second one.
So, did they know each other before and had been doing this a long time or were they new partners? I'm asking because:
It made no sense for Blondie to ditch Tuco just after two times. (In terms of money)
They both knew Angel Eyes and Angel Eyes was also familiar with Blondie (he says "would you talk").