Since I fly the treacherous, brutal , "no route for you" skies of the East, specifically the Northeast...
Here is how it goes: it will change. In most cases what you file is not what you will get. Sometimes it is to help you, sometimes it will not, so vigilance is required. If you are afforded the flexibility to take another route, once you get in the air you have more control over the situation, but don't be surprised if you are on the same route you accepted and have to divert for one reason or another. I have even had Cleveland Center on the phone about this. So, play it ethically. I would not buzz around the NE taking everything they told you, but there are a lot of options for diversions in the NE.
The question you asked has happened to me before. I was departing out of a control agency that I was not familiar with so I was not familiar with the flows. Three rejected flight plans. I could have gone VFR to start, but thunderstorms along my route and destination I was hesitant. Finally accepting their routing, it was basically the good word of tower I took to get me out of there and start negotiating in the air. I had time on my side, diversions planned and expected fixes planned. Once I was somewhere over Wash, they tried to give me an airway that would have put me in a minimum fuel situation, and I spent the next five minutes clogging up the frequency because of it. Grudgingly I accepted and found the last fix I'd stay on the airway before I knew I needed a turn to my destination. The tension helped though, I was cleared direct with the next controller, about 50 miles from my destination.
You can get direct in a lot of cases. You never know till you try. Knowing the airspace and routes helps a lot, if you have that time. Learn to be flexible to your extent possible. Basically, plan well ahead, anticipate, have options, remember you are the PIC, negotiate, be polite, and be ethical. That is how I fly in the NE.