A little more specificity would be nice regarding the evidence.
Winterizing an engine is one of the easiest maintenance chores on a sailboat. I like to change my oil in the Fall, so I don't have oxidized oil sitting in the engine all winter. Other than that, it's just a matter of getting the water out of your raw water system. Remove the water inlet hose from the intake seacock, stick a double ended hose barb (Home Depot) in the hose, and attach about three feet of garden hose to it. Fill a bucket with glycol based RV anti-freeze, stick the hose in it, and run the engine until you see pink water coming out of the exhaust port. Then run another gallon or two through it (important...stopping when you first see pink is NOT good enough). And, you're done.
I live about three minutes from one of the best sailboat service marinas in Michigan, but I don't let them touch my boat unless I lack the ability or tools to do a job. Luckily, that only happens about once every 10 years. There's no way they'll be as careful with my boat as I am. The internet, and excellent forum contributors like MaineSail have truly revolutionized DIY boat maintenance (although I'm surprised at how many people I talk to in my marina don't take advantage of it...baffling).
Oh...and the answer to your question. Yeah, you should be worried as to whether they did the winterization on your engine. I wouldn't think they'd put their best man on a job that easy. Not much you can do about it at this point. You might as well just forget about it, launch it, and run it. If it runs right and doesn't leak, you're golden.
Or...run it on the hard, first. Use the same technique I described for doing the winterization, but instead of filling the bucket with antifreeze, just fill it with water. You can run the engine as long as you want, as long as you keep water in the bucket. Ideally, run a hose from a faucet, and have someone filling the bucket (nozzle on hose for control) as it depletes. If you don't have a faucet nearby, start with several buckets of water, and fetch more as the motor runs. NEVER run a hose straight from a faucet into your engine, as it can cause damage. Use a bucket, so your engine's water pump does all the work. So, run it on the hard, and if all is well, launch it.
If you're in the Muskegon area, I'd be glad to show you how to do. Send me a PM. There's a large marina here, that seems to change owners and/or management every few years, but always ends up with another bunch of scoundrels. I would NEVER let them work on my boat.
