1992 Ford F-150 Throttle position sensor

I took my 92 Ford F-150 to Tires Plus to fix brakes and because it idles high. They said it was the throttle air bypass and replaced the idle air control ($227.99). It was running and still idling high but not as bad. Then they called and said it wouldn't crank. Now they are telling me it's the throttle position sensor that needs to be replaced ($199 p&l).
1. Shouldn't they have known the sensor was wrong when they did the initial inspection to determine the problem(which we paid $10 for them to do at their suggestion)?
2. If it was running when I brought it to them, they worked on it and now it's not running how is that my responsibility to pay for?