This issue sounds like it has little to do with the mage class itself.
My sensation is that there are personal issues going on. I very much doubt it is one sided. I don't know either of you, but as we only have one side of the story to go on I'll keep out of that side of things.
What is telling is your response to the players attempt to have NPCs find out information for him. My honest to god reaction to this is, what is the problem with that? That is a huge opportunity for endless amounts of intrigue, plotting, betrayal and broadening of your adventure story lines. Simply handing the money back and saying we couldn't find out anything is a lost opportunity. At the very worst the NPCs have tried to find out information have they not? So they have done their job. So don't hand anything back. You're going to take them on to get your money back? You do realise who they are... right? Well, okay then! Chaos ensues.
But you could do oh so much more with that door the player has opened.
It seems to me perhaps that you feel a little out of your depth as a new DM. I'm guessing you are a new DM to 4e at least as you don't seem to know the rules (I like to know the rules as a DM so I know when and how to bend, break and ignore them completely ... they are, in the end, very good suggestions!), and perhaps this is a part of your feelings of frustration towards the player who obviously does know them and is constantly throwing you curve balls. How you receive those curve balls is the most important part of being a good DM. Enjoy them I say. But make sure when you take them and throw them back they are laced with some good healthy venom. Your players should have a devastating effect on a DMs plans! And the DM should devastate them right back! Not in an adversarial way but in a



for tat making sure that the players are pushed to the limits and as such feeling challenged, which is part of the fun.
To me the DM philosophy "Say yes to your players" is the heart of what makes 4e (potentially) such a great version of the game. But a wise DM knows that really that philosophy is very often tempered with a "Yes ... (evil pause) ... but..."
So yes, your ploy to have details of the puzzle revealed via NPCs has worked! But ... But what you don't tell them is the NPCs that the mage paid were all slaughtered when they asked the wrong question to the wrong person and set off a series of alarm bells amongst a very powerful and dangerous hidden society that has a strong interest in ensuring people asking such questions are removed from amongst the living. Of course they tortured these curious fellows and of course they talked before they died. And so they learnt of the mage who paid for those questions to be asked. And now having slipped into the skins of the mage's now dead contacts they make contact and tell them half truths which will lead them closer to their goal, but also into a deadly ambush/trap/both. If that wasn't part of your world/story before ... who cares? It can be. You're the DM.
Magic Missile targets creatures. But if you can target a creature with it then why not something else? That is a decision for the DM to make. Things like that are covered in the DMs Guide. It's something I would definitely allow without even thinking about it. Would it always work? Hell no. It might sometimes if I thought that it would be cool. Sometimes it would do nothing. And sometimes it would land the mage in a whole heap of hurt.
[sblock=For Example]"Yes, something happens when you fire your magic missile at the statue! The seemingly dead stone eyes flare to light, locked immediately on the source of the force that awoke its ire. You feel your will locked into a battle to the death with a furious alien intelligence that is hell bent on your destruction ... in game terms ... you are currently stunned. You are currently in a mini challenge which requires 3 successes before three fails. Each round you remain in the challenge you take 5 psychic dmg. Any fail will be a catalyst to a worsening of the situation. As your mind touches this alien consciousness your mind is swept away to another place. You stand upon the shores of a sea red with blood facing the high jagged cliff. You sense the alien presence looming over you from the waves, reaching towards you. There are three caves in the cliffs. From the cave to the left you hear the screaming of a new born baby. From the middle cave you can hear a group of youths reciting a familiar dirge. From the right cave you can hear the laughter of a woman. A figure stands high upon the cliffs arms raised to the storm that rumbles overhead. When I come back to you I will need for you to tell me what it is that you do. You can ask about one of the features I have described. If you make a hard DC Arcana check you can ask about two. If you make that check and then make a hard Insight check you can ask about three. Then I will need an action from you. If you hesitate it will mean your character is in shock and we will pass on to the next round. (DM takes out sand hour glass and flips it over). Now ... the rest of you see the eyes of the statue flare to life when the magic missile strikes. You also see the mage instantly freeze where he is in a most unnatural, unblinking pose. But you can see the horror in his eyes. What do you do?". [/sblock]
Someone wiser than me on these boards once said that the real tension of a trap does not lie in discovering whether there is one or not. The real tension begins when the trap is discovered. It is then the tension builds as the PCs try and figure out what they need to do about it, or how to by pass it/disarm it without burning themselves to a crisp ... which of course is a great moment to say "And then ..." and of course something else happens which makes the trap truly dangerous so that the PCs are torn between dealing with the trap and this new situation.
So, my suggestion would be to enjoy the challenge. Enjoy the challenge of making it seriously challenging for your players, and especially for your mage.
Edit: I am curious to know how a mage (who will typically have 8 strength and 10 dexterity) managed to shove, trip or push any one into the path of anything.