Again, that's not true. Scouting his boxscores on a different league is not that different from scouting on your own. You have stuff that won't change much, like FT% or game rating, and checking his opponent in a different league is just like checking who he was playing in your league... It's not like the teams in your league are all the same.
I've already gave an example - Adam Morisson. Is there any relation between his abillities in the UNCA and the NBA? No there are none.
Except of the free-throws, which is one of the less important skills, if not the least significant.
And slow it down with the "real world" argument. I agree that there should be a deadline for playoff transfers further away from the end of the regular season, but in real life this episode of your opponent having a new player you haven't heard of before is not unimaginable. Lots of teams buy players and insert them straight into the lineup for the next game. In the NBA you can argue that there are few players good enough to play there that teams wouldn't have heard of before, but you're in an israeli div III league, so there are hundreds of guys who could play there.
This is absurd. When and which player had been bought at any league just before playoff (or even at the middle of the year) which was the most expensive at that team?
Even if you will find a rare case, it is just that.
It is far from current status on BB, where it is being exploited regulary.
Take soccer (football), for instance. If Man U or Liverpool buys a new player to put him in the starting lineup, he's likely to be a top caliber, international player. In that sense, there should be plenty of info to scout him on. That in general may apply here. If a team in a top division buys a 200k center, he's likely to come from a good team in a good league, so his boxscores there will be meaningful. On the other hand, if Tranmere Rovers gets a new kid from El Salvador, chances are nobody else ever heard of him before. In this analogy, the Venomous Scorpions can be Man U, you are Tranmere Roveres (no offense to them)
Give a name of a player that had been bought by those teams and had been the most expensive player (and by far) on their roster.
Again, even if you will find a case, it will be a very rare case (unlike current status at BB-game).