If a customer is inquiring about price over the phone or that seems to be their main concern instead of the job it's self then that's a big indication that they're going be cheap.
I wouldn't recommend walking away with out saying anything even if the person is a pain like that one lady. Try and be professional/ friendly about it because there are lots of ways for people to damage your reputation on the internet now.
Why would she hire another lawn care business when her husband owns his own lawn care business himself? Did that make any sense to you?
My son had taken a flier off our mailbox early in the spring where the guy had written a quote to mow our yard for $35. I didn't learn about it until later and told him next time to call the guy and have him come mow as the cheapest I would do our acre+ for was $45 (that's my buddy price) and his mom hasn't been paying me that. Then I got a quote from a guy who said he'd do it for $25 just to get into my neighborhood. Though I'm sure he would have done good in the beginning, we all know how that kind of bidding will end up.