How would you design these postcards?

[Kurt]

I don't think the colors or font are important. Black and white is what I'd use. It's the offer.

I'd say "Mikesbikes.com just became available! Call 1-46-567=-3456 to see if it's still available. This letter is going out to 5 Mike's Bikes shops across the country. First call wins!"

Maybe on the other side say "When customers go to Mikesbikes.com.....will they find you or a competitor?" 

Everyone wants what they can't have. Everyone wants what they think someone else wants. You'll probably get at least one call. If not, I'd call them, assuming the price of the URL is enough to justify the hassle.

Somewhere else there was a conversation where a person was offering his marketing services to a business owner
where he was familiar with and said he wanted to tell them if they didn't accept his services he would have to offer his services to the businesses competitors.

You replied that this would just make you angry if the marketer threatened you like this. To me mentioning other competition is using external leverage. Is it because of the personal connection or face to face that this would upset you and how to not P.O. people using leverage?