How do I tell which type of engine oil the mechanic put in?

My 2002 ZX3 is to take 5w-20 semi synthetic,
I asked my garage to put in fully synthetic, MOBILE ONE (what color is MOBILE ONE?).
I walked into the service bay and caught the mechanic filling it up with the
default 10w-30 regular oil.
I complained to management & mechanic was to drain 10w-30 & replace it with what I paid for.
How can I tell if this was really done? The shop is a local garage in about which I have never heard a bad thing.
Any damage if they left the 10W-30 in the engine?
Thanks, in advance for any useful responses.
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Watch them do it. If they give you a hard time about looking over their shoulder, LEAVE.
Shops who do it right, will have no problem you watching, within reason. The best bet if you can is do it yourself. For a small investment in some ramps, an oil wrench, you can do it yourself. I used to until I had back surgery, so no more for me. Or you can always take it to the dealer.
Good Luck!

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