If there's 1000 wallets that only transact with each other and never (or rarely) with other wallets, it might be possible to identify them as an island in the transaction graph - see [1] for an example of automatic graph clustering (I think the image is communities in facebook's social graph, but the same algorithm could be applied to a transaction graph)

Of course, whether that behavior would stand out depends on how other users of the system behave.

[1] http://www.ece.umd.edu/~wenjunlu/images/gephi.png