I look after my wife's car, our childrens' cars, my sisters-in-law cars and my own car. Back in the day of plugs and points I used to do my own car servicing including adjusting the timing. But, appearance is everything. I do a "visual" test on all the aforementioned cars together with checking the oil, tyre pressure, lights and wiper water. Then I hoover the living daylights out of the car and follow up with a power wash (with emphasis on wheels/tyres) and then shine up the inside with beautiful smelling stuff. Connect the seat belts in the back and drivers seat - just do what you are advised. The following morning I bring the car smelling like Miss World's perfume to the Test Centre. Todate none of "my" cars failed the test.
I have seen cars arriving at the Test Centre with more mud than a tank on the Somme. After mechanical/electronic workings, it's all about appearance; I reckon that's what Fergal Quinn (best sales person ever) would have said.