Surely you can simply log the 'trial' lessons in a newly purchased logbook as dual instruction Sequences 1-13? You might not be getting the sequential lesson patter from the pilot/instructor but you are flying dual with a person qualified to teach you how to fly yourself. Make the man work for a living and get him to patter you properly, treating each flight as a lesson. There's only one reason why the instructor should take a casual attitude and treat the flight as 'just' a trial and that's a bad one.