Unconscionable for the steering not to be tight and properly seated in the helm. I am assuming from your post you have a Teleflex type steering. If it clicks hard into place and you can't pull it out with turning the steering wheel you are OK.
Go to the back of the boat and look at the adjusting holes where the large mounting bolts attach the engine to the boat. Do any of the unused holes show signs of the engine being mounted through those holes? It is quite possible he didn't put the engine in the proper place.
Is this a power trim or manual trim motor?
OK now you say the the engine idles bad. This would have nothing to do with the engine set up. I'll tell you where to look and the probable problem.
Inside each carb is a idle jet. In actuality this is a long very thin tube. It is restricted (jet) inside and also has some real tint vent holes drilled in the tube. What you will need to do is totally disassemble the carbs and remove this idle tube. Carefully clean it with some carburetor cleaner and a rag. Examine the idle tube with a magnifying glass and you will probably find some very small cracks between the vent holes or leading from the vent hole. Unfortunately this is a very common occurrence in these carbs.
You will need to replace the tubes with new ones. They are not expensive. I would also replace the gaskets as well including the intake gaskets. Then after putting everything back together you need to have the carburetors synchronized. This is very important.
I run into this on a regular basis with the 40/50 hp Honda engines.
I also recommend after each use you drain each carb via the drain screw on the bottom of the float bowls. I would also recommend using a qualified shop to do the repairs, someone familiar with those carbs that has the proper tools and service manuals. If they don't have a synchronizer tool, find another shop.
Post back how it goes.