Anybody who tells you they got into the F1 paddock, paddock club, pit lane, or grid with a fake pass (in recent history, anyway) is lying to you, pure and simple. I should know, I've been in the paddock club and pit lane for the US Grand Prix twice, and I have a large collection of F1 passes.
The passes that get you into these areas are:
* Impossible for an ordinary member of the public to copy (full color printed on thick plastic with large metal and/or plastic buckles, customised for the specific area and day you have access to, with embroidered neck straps that are also customised in the same manner)
* "Chipped" so that they can be read by turnstiles that are placed at every entrance - even the drivers themselves have to wave their passes near the machines to get in, so even if you managed to make a perfect looking fake pass, it would get you nowhere).
F1 security is also absolutely first-rate. They check every person entering the restricted areas, examine your pass carefully before issuing you a wristband that can't be removed without damaging it, and holepunching your card to show you've had your wristband issued (after which point, you can't give your pass to a friend). They also check everybody's bags carefully, and even pay attention to whether you're carrying beverages in with you (because those must be left outside - only sponsor beverages are allowed to be consumed beyond the turnstile). To suggest that you'd get past security with a fake pass is laughable.
Oh, and F1 security staff are the same at every race - they fly around the world with the rest of the F1 circus, to provide consistency and ensure they're familiar with the rules and procedures. Locals need not apply.
I'd be happy to provide photos of some of my F1 paddock club passes as proof I know what I'm talking about here, and they're not even as fancy and complex as the ones that get you into pit lane, let alone the all-access passes.
As for getting in as a journalist, forget it. F1 journalists and photographers have to pass a very high standard of accreditation to get into a race, so unless you plan on starting a new career so that you can get into races a couple of years from now, that won't work. Marshalling will usually require you to have significant marshalling experience in lower formulae, and will get you access only to the areas that you as a marshall need to be in - which the paddock won't be.
If you want to get into the paddock club, you either need to become rich, or have exceptionally good contacts. If you want to get into the paddock / pit lane / grid, doubly so.
Edit: Here's two pics from 2005, showing the turnstiles set up in Monaco. The same equipment is used worldwide, though.
I should also note that the turnstiles record the times that the bearer of each pass enters and exits, won't allow re-entry until an exit has been recorded (to prevent passes being handed through fences to get multiple people in), and AFAIK are capable of recognizing guest passes as children of a particular master pass, so that if the master pass holder doesn't show up, their guests aren't allowed in either.