Riiiight !!
Well, personally I would be very suspicious of that sale. I think it is far more likely that it is just one of 20 or more balls that were produced for the match. Most likely it was never even used.
Think of it like this. If you were a Portugese fan and you had caught that ball from the Beckam free kick, would you sell it?? Given that it would be very hard for you to prove it was that actual ball and that it will have quite a large sentimental value to you as a fan. Now compare that likelyhood with someone that has managed to get hold of one of the balls, a ground employee for example. The ball, having never been used will mean little or nothing to you. So you're much more likely to try and scam someone with it.
Just my opinion of course.
GTM