Use condoms!!!

Why is life so difficult ?!? ;-) Ok so it isn´t all that difficult but boy trying to be a parent and a good one at that definitely IS ! After buying my train ticket for tomorrow and surpricing Halldór at school with iron bru and a chockolate muffin we headed to Blackwells (bookstore)... I allowed them to go downstairs to the childrens section whilst I preused japanese books upstairs and made grand threats of removing privileges were I to find them fighting or misbehaving when I came down. Well I came down and they were perfect, so polite and well behaved just browsing the books, so I decide to reward them with books. They both had books in mind (here is where I start doubting mself) but I quickly persuaded Elena to go for a different one, one with letters and stickers and then proceeded to get Ragnar to change his mind about his book, it was on ancient egypt but too hard for him to read and cost 15 quid, so I found him a simpler one on egypt and another one on mummys. At which point he couldn´t decide.... then he brings harry potter and the prisoner of azkaban, and after having him read me a bit I say sure but lets start with number one and then I ´ll get you the others... plus it´s thinner! Naw..he doesn´t like that... so in the end I´m looking for books bringing new ones to his attention and he´s all bleah, finally I dig up the goosebumps series remembering that it had one book on mummys.. naw he´s not intrested in that but says "I like this one" about another one in the series.
So off I trot, happy with life and myself, to buy books for my children only to return to him looking at me teary eyed and saying he didn´t want that one. At this point horns are sprouting from my forehead and steam is coming from my ears. He tends to do this a lot! Decide something then want to change his mind later and becomes all sullen and withdrawn when it´s not possible.

My dilemma is: was I doing the right thing in trying to manipulate him towards what I though best for him? I did stay in the same genre and had no qualms about the type of story, all that I insisted on was that it was the first in a series, easy enough for him to read and within my financial capabilities. Seems pretty logical until I think back and figure out that all this could probably have been avoided had I just agreed to buy book one or two he chose originally... :-(
What do you think? I don´t want to buy him something that´s not going to get read or used but I do want to encourage independent decision making ....
And here I am overanalyzing again, right?? ;-P
Any thoughts?