Does it really matter what his business model is, if its even his business, or how much in tips he's making? Maybe he only gets to keep tips? We don't know and frankly its really none of our business. Would we ask these sort of questions of other businesses we deal with every day? Would you ask a bartender if he works for tips only? What about their hourly wage? Would your tip change if you knew the bartender was making $100 per hour? What about if they were given a percentage of the totals sales during their shift? How should any of that factor into a tip?
It was always advertised as free and tipping was completely up to the individual. I recall from previous topics that $10 is often suggested as a recommended tip and that seems like a reasonable starting point. I don't believe gouging is the norm. Besides nobody is forced to buy anything and its not like your stuck at any one place for long. The reviews speak for themselves. Most find it to be an enjoyable experience and good for Lenbert if he happens to be making a decent living delivering this experience to visitors.