troubleshooting, tires, alignment

Pretty good when you know exactly what you need. I've started losing power to my engine, and now its begun to die. I took it in and they said they could not re-create the problem and so couldn't do anything for certain. They replaced my thermostat, fixed my alignment and put on new front tires though. After some quick research, it seems to me the first place I should be looking is my spark plugs or fuel pump. Lack of spark or fuel is likely the cause of loss of power, says the google. Why didn't they say anything about these parts? Why didn't they ask me for more details on the symptoms rather than just taking my $400 and handing the keys back.