This happened to me just recently also. The guy did not like my .COM asking price and he never contacted me again for any kind of further negotiations after just 2 emails.
But then 2 days later, i discovered that the .NET version of my domain was suddenly registered, with YEAR 0. My .COM is YEAR 9.
My domains are never parked. Being "lightly" developed, they all show up on Google. Because this specific .COM domain is a two-word generic keyword domain, when he regged the .NET it is a sign to me that he wants to go head-to-head with me on Search.
If he is a serious web developer, i don't know if it will help his cause that two identical domains will be showing up on Google and confuse his customers. So i'm not sure why he would reg the .NET in the first place.
The more you develop your .NET, the more i develop my .COM. If you are a legit business and eventually wins the SEO war, some of your traffic will end up in my turf and hopefully i can monetize them to pay-off the renewal costs forever.. plus profits. So my .COM will be like your .NET's evil twin brother.
That's the full-blown web development war scenario.
In terms of regging the .NET just for bluffing purposes during price negotiations. Well, if you think it is worth 8 bucks to see how he would react, you would have to tell him that it was you who regged the .NET. In any case, if i was the COM owner, i probably would also spend 8 bucks myself (or 1.99 Godaddy transfers) and wait another year just to see how far you would go with that .NET. If it's an empty threat, i am looking at your .NET to eventually drop-out or remain undeveloped. Otherwise, you would have to spend time and effort to develop it to earn legit status. And if that happens, the situation will just end up with the SEO War i mentioned above.
So in my opinion, you can pay the bluff and reg the .NET and see what happens. Or walk away, if you really don't want to pay the man what he wants.
Merry Christmas.