A good swimming pool technician will,at least occasionally completely disassemble the filter and clean it even if you have a backwash valve. If you have a sand filter,it may be years before it needs to be taken apart,and a cartridge filter HAS to be taken apart to clean. But a D.E. filter can be backwashed 2 or 3 times but should be fully disassembled every third or forth time. Many service techs charge a fee for this and simply take it apart EVERY time. Also,if D.E. powder is accumulating in your equipment area,a good pool technician will offer to lengthen the backwash plumbing and/or install some type of hose to backwash D.E. away from your swimming pool equipment area. I have seen D.E. accumulate to the point where a relatively new(2-3 years old)heater has to be replaced because the bottom of the heater and the burner tray disintegrated from corrosion. In this case,the homeowner had a home warranty policy but they would not cover it because of improper drainage. A replacement heater was over 2,000.00!...Same goes for dirt or plants like ivy growing over your equipment....a good service tech will at least alert you to this.
Besides checking the OTO and PH levels,a good pool service technician will also check your alkalinity and conditioner levels. A high conditioner level will cause incorrect alkalinity readings which over time can corrode metal such as copper plumbing...even if you do not have copper plumbing in your swimming pool,don't forget the heater - the heat exchanger is made of copper..expect to pay from 400.00 to 1000.00 to replace a leaking heat exchanger depending on model and size of heater.
A good swimming pool service technician will know of the latest
trends in equipment and make you aware of new products that may benefit
you and also things like rebates from the manufacturer or another source
such as your utility company. For example,DWP is offering 1000.00 rebate on energy efficient pumps IF installed by certified installer (as of March 2015)
A good swimming pool service technician will also have a few tools in the truck. At least a few screwdrivers,some wrenches,and a rag and some lubricant for o-rings. A REALLY good tech,(like myself)will also have things like a CO2 bottle to blow out plumbing lines,a manometer to measure your gas pressure,basic PVC and copper pipe fittings,extra o-rings,pump seals,some heater and remote control manuals,and a few specialized tools like a motor shaft wrench and a backwash valve puller...of course,most pool men do not have the room for these tools in their truck because of all the chemicals and cleaning equipment they must carry.
A good swimming pool service technician should also have general liability insurance or at least a bond. One thing I would like to add:depending on your day of service,there can be 5 months out of the year with five service days that month instead of four...so if you are paying by the month,try not to get too upset if your service tech takes a day off once in a while....remember the other months when you got a week for free!
And last,but not least - If your swimming pool service technician does the opposite of the above criteria, its quite possible he or she simply does not give a damn about you or your pool or is simply not a professional...pay a little more and get a professional it will save you in the long run...I personally see the damage caused by some incompetent pool techs that they pass on to the unsuspecting customer.......even myself sometimes in the past more out of ignorance and not hostility... ....some guys out there cause more damage than good many times more from laziness than ignorance