Get the certs if you want. I choose not to for the simple reason that I don't have time to. I do my best to keep with proper pruning standards. I admit to hacking a few back in the day when I needed the money but only when I needed it. I don't walk away from it now either. I try to educate the HO and if they can't be swayed I'll rattle off some price 100 times what it's worth and tell them that's what it'll cost for me to do what they want. I've got more work then I can get to doing proper work without the certs. I will say that some contracts do require certified arborist. They are few and far between around here though.