One of the things I would always do with my clients when I worked behind the chair was go through the products I used on them during styling at the end of the appointment.
I understood that they wouldn’t always buy every single thing I showed them, and I could usually gauge where they were with their product usage by just having a quick conversation with them.
After explaining why I used what I did, I would usually finish up with, “. . . but if you could only choose ONE, I’d choose ______” so they didn’t feel pressure to buy it all. I’d focus on the product I thought would help in the most dramatic way with their hairstyling, so they could really see the value in using the right products.
When it comes to tools, I completely understand that it’s a steep investment to purchase a really fantastic blow dryer, curling iron, and flat iron EVEN before you add products into the mix! So, if you could only choose one, between a blow dryer and a styling tool like a flat iron or curling iron, which would I steer you in the direction of" 
Here is what I would take into consideration: your texture, your lifestyle, the length of your hair, and your styling goals.
If your hair is extremely thick, long, holds onto water, or has any trait that makes you dread drying it, I’d tell you to invest in a high-end dryer. You won’t believe the difference in using a great one versus a cheap drugstore dryer. I’d also recommend you try ...