I have worked with loads of concrete guys. Some are laborers and some are artists. Which one do you have? Get a warranty. Matching concrete is nearly impossible.

Thanks for the input. This guy is probably more in the laborer camp but with an eye to matching (e.g., he mentioned this when discussing tuck pointing my brick house as well). He is going to be coating the entire side stoop steps -- not just the part that needs patching -- since it's impossible to match. He did tell me the re-coated side stoop would not exactly match the concrete stoop/steps he'd installed in my backyard because of the different product he needs to use in order to patch.

Any idea of what's a standard warranty?

Warranties unfortunately usually only cover workmanship and structural integrity and rarely aesthetics. I would ask to see some examples of the practice he is planning on implementing your project.