Camera Woes & A Ghostly Crow

Advice on what to do much appreciated!

I've had a couple of weeks without a camera; my little compact gave up the ghost after a couple of weeks of clunking & spluttering! I'd already decided I wanted to step up to a dslr but this forced the issue. I've been researching avidly for the past few months, and low & behold the one I wanted with an extra lens appeared on ebay... I waited with baited breath, conscious of ebay horror stories. I've never actually bought anything off there before but still choose to make my first purchase a major one...I had been watching cameras for the last 3 months & this seller had a good history.... 

The first thing was when someone messed up the address, just 2 numbers the wrong way round, but it meant an extra 5 days of frustrated anticipation. Last week I became the proud owner of a second hand Nikon D40, hopefully not too complicated but up to the task I require. They say trouble comes in threes....

The second thing was the marks at the top of the images... 

The camera came with a lens already on, so I took it off & cleaned it, looked inside, removed a blob of white material & a hair... similar result, tried the other lens... same thing... trawled the internet to find out about cleaning... tried blowing any dust out... slight improvement but the marks are still there. It seems I have dust on my low-pass filter... hmmm!

Anyway, during all this I got a lucky 'ghostly crow' shot, click to enlarge & you'll see what I mean. Well, actually it's a rook, but I didn't think I'd get away with the rhyme for rook I thought of for the title of my post (as in my camera's f*****d!) Rooks have grey beaks & longer thigh feathers, which can look a bit like they're wearing baggy trousers or cropped leggings. 

Back to my mucky marks on the filter.... it seems that with a bit of care, the right equipment & a steady hand I can clean the filter myself. BUT the camera forums have plenty of beginners tales of woe about scratching it  or causing more damage than their camera is worth... I'm scared to try, maybe if I'd had the camera a while or had let dust in myself... but this was there already & it will cost me for someone else to do it, plus the local camera shop doesn't do digital repairs so I'll have to travel further afield.

I emailed the seller who said he'd just cleaned it & it was in perfect condition when he posted it- it must have been me! Hmmm, explain the hair & the fluff then! Maybe he did clean the filter... maybe the marks are on the sensor itself.... i'm more panicked & annoyed now!

I've been working my way through the features of the camera bit by bit... getting comfortable with it & working out what's what. So far have stuck to using one lens, apart from when I first tested them out.... then yesterday I tried the 70-300mm zoom... oh boy, did I have fun! 

I'm not claiming any technical skill, but I was squealing with delight when I abandoned any automatic settings & worked different little bits out.... I'm going to enjoy this camera even more once I get those marks sorted out, I'm just hoping that there is no third thing that goes wrong!