Car seat safety help!!

I went to a car seat safety clinic today and I was less than impressed. From my research (though only from the internet and classes) I have been told very conflicting things.

1. The middle seat is the safest. That is what the class said and what my research said was true also. At this clinic, however, they insisted I move her to the side because my vehicle is older and only has a lap belt there. Further internet research.(and my prenatal class) shows that this is fine if the carseat says it's is okay (which Mine does). So do I keep her to the side or move her?

2. Only items manufactured with the car seat should be in the car seat. This was very clear in the class and internet agrees. However at this clinic the blanket I had around my daughters head to support her neck was removed as a suffocation hazard and I was told to get one of those neck pillow things that go behind her back. Yet again both are completely opposite. Which one should I do?

And then they kept switching the straps on my daughter carseat to the lower notch. I informed them that the notch it was on was below her shoulder. They didn't believe me and then once I put her in it the way they suggested, did they decide I was right and put it back.

I went to this clinic because I thought they were professionals. But they are contradicting everything I have read and been taught in my classes. Any opinions would be loved. I am running around like a chicken with my head cut off because I have no idea who is right or not.

(Also the gals inspecting / changing the carseat didn't seem like professionals at all and had to have someone else check their work. They also kept saying "I am not sure" or "I am pretty sure" The base was also not snugly strapped down so I had to tighten it. )

Help please.