A friend of mine runs his own printing company so I get him to print my stuff for me. I get a massive discount under him that a normal punter wouldn't get.
So I don't mind acting as the middleman. If I charged for the design and they got it printed it would work out dearer than me just looking after it and I still make a bit extra out of it.
I don't see it as underhanded, it's just easier to bulk order with my printer for discount and the savings are passed on to the client, even though I make a bit extra from it, which is rightly so, as I have to pick them up and deliver them, so there's my time for that.
In the final email when the client says "That's good to go" I send a reply saying "Hi <client> Please ensure all details are correct, any errors or omissions are your responsibility."
I always get a message saying "Hang on I'll get my other half to read it".
Once they give a go ahead from this then it's all on them.
The good thing is though - I can get 10,000 a5 flyers overnight. So my service in providing print is valuable to my clients as they wouldn't get that overnight service or the discounts I can avail of.