Question

Hello and blessings,
A strange story, and a strange question to go with it.
 
A fitness trainer offered me five sessions for free. His claim is that once I start, I’ll continue (for payment), and in his opinion I’ll continue specifically with him. I explained to him a hundred times that I won’t continue because I don’t have the money for it, but he insists that he’s willing to take that chance. Now I know, practically speaking, that this trainer is mistaken and that I won’t continue. I’m really almost completely sure of it—it just doesn’t fit my budget and I don’t have extra money. So I feel a bit like a fraud accepting the free lessons from him, because it is obvious and known (and was also said explicitly) that he is simply overestimating the likelihood that I’ll continue to paid sessions. On the other hand, if he wants to give me gifts (there’s no reason this should happen, I don’t know him, we met by chance at my child’s kindergarten), who am I to tell him no? 
 
Now as far as whether it feels pleasant or unpleasant, that’s less the point, and I do want to go to him because maybe it will cause me to keep exercising a bit (just not for payment). And if he insists that much, then fine, good for him, and maybe he has other considerations that he didn’t reveal to me (to gain experience with couch potatoes like me, maybe he expects that I’ll recommend him, maybe so he can say that he trained people from my sector and lifestyle, maybe I don’t know what, maybe he is giving me charity—which I’m not interested in receiving). The question is whether this is permitted for me, or whether, if I personally think he is mistaken in his assessment of reality, I cannot take advantage of his mistake in order to receive something of monetary value from him.