One must consider two factors - the act itself, and any premeditation. In this case, there was no premeditation, so a prima facie case fails if that was the sole criterion. However, there is the act itself, and in this case, it was perpetrated not by the (self) accused but by his girlfriend (whether with or without the knowledge of his wife), without any direct solicitation by the accused and apparently without his intention being to cause the purchase. I think a caution would be appropriate, and congratulations on the choice of girlfriend.