Even if its people with expensive and rare Beyblades, it doesn't mean that they'd shell out a lot of money just so that they can have a trade verified.
In fact, their rare beys would be sold out in a moment. A seller usually looks for the best deal he can get. And as every seller will tell you, trading is extremely unsafe(and hence not something they prefer).
So while these sellers get trade offers, they are offered prices too. So they'd usually go for the safer, more reliable method- Selling over Trading.
So that is a reason why such people wouldn't really opt for the system you mention.
Your intention is cool. If such scams could be prevented, it would be awesome. Unfortunately, such scams can't be prevented in this manner.
But for now, as the sellers have always said- Its always advisable for the trading parties to know each other well. Once the mutual trust develops, and both parties have a good track-record, trading can be considered safe.
Team IB Revolutions
Thanks to N0body for the avatar and Synth for the signature!