I've gotten really good at convincing my wife that i NEED things and use big long technical words to describe why. most of the times that works, but if it doesn't i just get really persistent and annoying about it. for instance, every time i see something similar to what it is i'm wanting, i find some obscure way to mentions that i still want that. eventually (may take several months) she gets tired of hearing about it and says "whatever then go just buy it then". then i'm in the dog house for a week or so because i'm supposed to know that "whatever just buy it" means "don't you dare buy it". then i buy her something nice (and i mean something worth at least 25% of the cost of whatever i am getting) and i'm usually in the clear within a day or two. I never lie, I just plan out how i'm going to accomplish something, then do it.

You need to have patience, be able to deal with the aftermath and be willing to do something in return. but for heaven's sake don't go behind her back to spend her money. that is what makes men look bad. a real man is respectable and honest.