These inexpensive strips are a strong sales tool for fluid flushing.

Why do brake fluid changes?  For several good reasons.  Corrosion and contamination of that intricate and expensive ABS and DSC hardware is to be strenuously avoided.  Another factor is the elevated operating temperatures encountered in the high-performance braking systems BMW uses, which makes maintaining a high boiling point critical to safety.
In the U.S., this is a relatively new service item that the average motorist has never heard of.  So you’ll need a good approach if you’re going to convince him or her to have it done and thus save big bucks in the long run.  First, pull the owner’s manual out of the glove compartment and show the customer where it appears on the service interval chart.  Explain how disastrously expensive internal corrosion can be.  Also, you might want to keep those “Wet Check” brake fluid test strips handy, which you can staple to the repair order, or you could invest in an electronic moisture detector.

Another item that is very helpful in raising customer awareness is an electronic brake fluid tester.

Many pieces of equipment designed to make this job fast and simple are on the market.  Or, you could do it manually.  Regardless, just make sure never to let the master cylinder run dry in the process or you’ll have to bleed all four corners over again.
Then there’s brake fluid itself.  Modern DOT 4 glycol is excellent because it has a high boiling point and the ability to hold lots of moisture.
BMW specifically warns against the use of DOT 5 silicone because it has serious — and dangerous — drawbacks in terms of seal life and water slugging.
BMW has published the following on what it requires in its vehicles:
“Brake fluid, (glycol-based) as used in BMW brake systems, must conform with the following requirements:

• High boiling point
• Good low temperature resistance
• Low compressibility
• Corrosion inhibition for all metal parts inside of brake system
• Compatibility with all rubber parts used in brake system

These requirements are fulfilled by reputable brand name DOT 4 brake fluids.”
But why not keep your customer’s vehicles all BMW?  While you’re buying pads, rotors and other brake parts from your local dealer, add BMW-branded DOT 4 brake fluid and you’ll be sure you’re giving your patrons the right stuff.