If they cant figure out if its a starter problem vs alternator problem, they shouldnt be working on it

Being that, u said it has trouble starting, can u give us more details about it?

Like do the dash lights come on, do you hear any specific noises, are u able to jump it? How long did u drive it for when u got it back?

Isnt there usually another cap right next to the fuel cap for exhaust fluid? Or at least another door for it

Disconnect the battery so it wont be dead