OP, for some reason, I woke up this morning thinking about your post.
My first reaction was to say "Don't get your knickers in a twist," but that's based on how I use "kiddo" and "sweetie." (I don't say "love.") For me, it's shorthand for "You're nice."
This probably isn't relevant: What came into my mind this morning was how I used to react to the words "girl" and "gal." In my 20s, I felt they smacked of both ageism and sexism, and got all wound up about them. But the people using them were innocent of harm, and suffered through a few lectures from me.
Bless their patience!
So if the terms are common where you are, don't waste your time protesting; let it roll off your back. I would also ignore it if you otherwise have a good working re1ationship with these folks. As a Realtor, you don't want to burn any bridges.
But if you are genuinely being looked down on or condescended to, or even if you just want it to stop, I think the best way to handle it is with humor. Your tone can range from gentle to extremely pointed!
Some suggestions, since I'm feeling creative:
"Does your spouse/SO know you call me that?"
"Does this mean I should expect an engagement ring?" (But not if your creep-senses are tingling)
"Oh, that is so
sixties!" (When Beatle-mania first swept the US, little girls like me used lots of Brit-speak, including "luv.")
Sweetie: "Just call me Raspberry - and watch out for the thorns!"
"That's me, half poodle, half pit bull!"
"Sweetie?! What are you on/drinking?"
Kiddo: "Good thing the grade school closed early so I could be here..."
"Now excuse me, I need my binkie/pacifier and a nap."
"Don't let it get out that I'm your kid! They might accuse us of conflict of interest!"
I hope this is helpful.