Have been doing DTC diagnostics for $15.00 and applying that towards labor if I do the job.
I will tell hesitant customers to go ahead and get their free diagnostics from these retailers, bring the results to me, analyze them and explain those codes
Most of those codes are already described, I proceed to explain that these stores are retailers and only interested in selling the most amount of parts/materials
possible.
I will then re-set the codes and if I don't get a code immediately tell them to just drive normally and bring it in as soon as they get a MIL.
90% of the time the customer will return, do a scan, get the culprit code, repair as necessary and have a happy customer for life.
Happy/Satisfied customers is my best advertising tool, so if it takes me 15 minutes to explain some of the basics of OBD 2, I find it worth it in the long run.