Any competent farmer or estate dweller who had Eb as a hired hand would fire him. Just like any competent sheriff would fire Barney Fife as a deputy. It's just how sitcoms are set up for laughs and crazy plots and gags. Yes, Oliver would have fired Eb-- especially when you consider he didn't want him at first, but, after all of Eb's pestering, hired him on the spot when he told where to get water to prime their pump and it's a long way to go there for a favor. "All right!-- you're hired!"
Often I'm not as bugged by all the loopy, scatter-brained nonsense spouted by Lisa, Kimball, Haney, Eb, et al, as I am by Oliver's always yielding the conversation to them, as someone else alluded to on this thread. "Oh, how can--" "That's the most--" "Oh, for the love of--" He ought to finish his thoughts and tell them to make sense or get the hell out of there. But, like not firing Eb, such craziness is just part of the show as it's set up.
He should have hit Haney in the head with a big stick after their first transaction and every time after that.