You can stretch F9 1:1 and tackle most rust with it. Fill a Zep spray bottle and you'll use 10 squirts on most little rust stains a house has. Or you can use Bar Keepers Friend, but it takes longer.
As far as pricing, I'm certain we're the most expensive exterior cleaning contractor in Kansas City, but I could give you 100 reasons why our customers don't care. People always ask about pricing and it's the 9 little things you do to the 1 house wash that customers are paying for.
I don't think there's an industry standard per se. If you don't want to use F9, I think Rust Remover Plus is a little less expensive and has a lot of great feedback. If supply costs or overhead are a concern stick with Oxalic acid. At the end of the day, it just takes a little longer to do the job 90% as well as the F9 or RR+.
Like they say, if it's not broke don't fix it.
As far as the "Authorized Applicator" designation, I haven't researched it nor would I probably. A before and after picture of a previous job will sell more than a designation in my opinion. Most people have zero clue what a designation really means to them. Check out a recent post we put on our facebook page about rust removal. The before and after pic got us a lead. Then check out our posts about being Kansas City's highest rated exterior cleaning company with badges from HomeAdvisor. Crickets. Not a word or a lead from anyone. Lol.