At my instructor seminar this came up in another way - the 100 hours I was claiming as an instructor in the past 3 years were 'inspected' to see if any of it was obvious gained as rental checkout supervision, as it could not be counted to the instructor renewal as it is NOT instruction. The instructor and "victim" must just agree who is Pi/c and only one logs, and it doesn't count as training. The only way it could count was if the rental checkout was designated as the instructor flight for JAR in which case it is p1 to the instructor and p u/t to the victim.
Can you believe some SYNDICATES think they can double log time (p1 and p1/s) between two PPLs just for syndicate checks! Hope their examiners spot it at JAR revalidation time!