Just tell her that if she's not happy with your work you will gladly restore her vehicle to its original condition!
Kidding, of course.
Are you familiar with Pareto's Principle? Most people refer to it as the 80/20 rule. 80% of your effort brings in 20% of your profits while 20% of your effort might bring in 80% of your profits. What I mean is that sometimes you put alot of effort in for very little results. This may be the case with this customer.
Is customer education important? Certainly. There does come a time when an upsell is no longer effective. I sell clothes for a living and not everyone NEEDS an extra pair of pants. Let's say a pair of blue jeans costs $50 or you can buy 2 for $80. Some people automatically wants both pair for $80; easy sale. Some people don't know about the deal so you explain it and you sell 2 pair of pants. The third person only wants ONE pair of pants. You explain the deal to them, they say no. You explain how it's cheaper in the long run and they save more money but they still say no. You FINALLY persuade them to buy the extra pair and then what happens? They come back first thing tomorrow and return them which costs YOU time and money that you could be spending with other customers. Make sense?
You're young and you're ambitious, that's great, it will take you far. Take enough time to see that not everyone needs every single service you offer. Suggest it, yes! Force them to buy it, no! Move on and make money from other clients.
