All of this seems to be responding to the complaint that Borrow Lenses' offered reward was insufficient, but I don't see any such complaint in the post. To my eye, it looks more like his complaints are a) that they misled him and in so doing caused him financial injury, b) that they falsely accused him of lying, and c) to add insult to injury, they spitefully refuse to do business with him after he took umbrage at their false accusations, despite the fact that he has dealt fairly with them and he is the only one who was injured in the whole affair. Points B and C really seem to be the crux of the matter — that is, it's not that they reneged on the promise, but how they treated him after they reneged — and it does sound like very unprofessional behavior from this company.
Also, he did not actually request $600 from them, but two free rentals. Unless this company is operating at a loss, the cost to them should be substantially less than $600.
> you would have been better off clarifying the terms of your agreement at the time
Upon being told "That sounds fair — we will give you two rentals free when we get the lenses back," what kind of clarification would a reasonable person seek? Based on Charlie's story, this doesn't sound like a misunderstanding, but one party simply going back on its word. (It could be that the exchange was actually less specific than it sounds in the post, but I think we're just dealing with how the situation comes across there, right?)
I still truly believe that being called a liar and hung up on trying to explain my position was an unnecessary line to cross when dealing with someone who had been consistently renting from them withut issue and had returned their lost gear notifying them within 24 hours of receiving it. But then again, that may just be me. :/