I like your wife....she's a smart woman.
Here's a thought....raise your minimum charge, so that when you give the discount, you can make the minimum charge you are currently charging. (When is the last time you raised your prices?)
If your min. goes up just $15 to $135 and you give 10% off, you're at $121.50. And then you are making $15 more on every minimum job that doesn't use the promo.
We just ran a promo for 50% off a single couch (which is normally $150, our minimum charge) and then 10% off any additional work they do at the same time as the couch promo. I thought we were going to have to eat some to just stay in front of our customers and keep some cash flow during the slow season. Sent it out via
service monster to all our clients. Completed 4 jobs as a result of it so far. One was $117.66. so a bit below our minimum. All the others added on.....really added on. 4 jobs, $3178.20 so far and at least 5 more jobs scheduled with add ons on top of this. Try it....test it out. I bet you most people will add on and do more than the promo (you always have a handful of cheapskates, but the rest should make up for it).
Subconsciously, people buy more, when they think they are getting a deal. I have heard this concept before, but didn't really buy into it. Now I'm kicking myself for not having offered this type of thing sooner. This was our first try at it. And since most of the people who took advantage of it were existing customers, I realize how valuable having some sort of a loyalty program could be for us.