I had this experience in the past where I came across a project I really wanted to take. I was so convinced I had what it takes to deliver it on time and deliver it with excellent quality. Of course, not to mention, the budget was interesting.

I placed by competitive bid on that project (it was actually 3rd from the highest bid) hoping that I will be awarded the project. With my bid in, I went on to make some quick samples, compiled a few related projects and sent these to the employer. I got no reply the following day (the project was still opened with more bids coming in). I sent another message to the employer not realizing that I became very aggressive already.

After a couple more days, the employer responded, 'your bid was interesting and I could have awarded you the project but I don't like working with aggressive people. Sorry, I have to pick someone else'.

I learned my lesson. One or two messages should be sufficient. Wait for a reply before sending another message (when the situation asks for it). Otherwise, leave everything to the employer. After all, no matter how good you are, showing some kick-ass portfolio won't count much; final decision is still theirs.

Provide what you can, convince them that you can and that you are the person to hire but NEVER pressure them with your aggressiveness or you are most likely to fail.