I don't treat them during the appointment time. However, I suggest they exfoliate with an exfoliating towel I purchase from Universal Companies for about $3 (& retail it for $8). It is vey effective yet gentle.
It can be used daily with your shower gel. Or I also offer a clear liquid made by Flora wax called Flora Flo. This is applied with a cotton pad/ball after bathing 1-2 times per day after waxing. This product works with salicylic acid. I have retailed both for several years and always receive positive feedback. I find explaining exactly what an ingrown is to a client and then how to prevent them sells either product !
In out industry there are 2 types of clients. 1 will listen and following directions and the other one will not. I have started offering this service for people who have been plagued with ingrowns for more than a year and over do it at home with home care. They come in every 2 weeks for a treatment but I dont extract any hairs and they have no home products to do more damage as well. I charge $20 to $25 per service and will discount to $15 as an add on post bikini/brazilian wax.
I created a treatment called "secret garden grooming" depending on the area i'm treating the cost is "$15-$35.........I agree with your description of clients.
I sell PFB Vanish in my salon which works wonders for treating infected ingrowns and bumps. If the odd ingrown hair is obvious for me to remove I will but the product is magic and I rarely need to do so.