Opening a guesthouse or bed and breakfast can be a emotionally rewarding way to meet people from all over the world while making an income – or it can be a money-draining, back-breaking attempt to keep up with the demands of the hospitality business.

On Wednesday, The Wall Street Journal featured a four-story mansion in Park Slope on the market for $4.75 million. The owner, Liana Paolella, initially opened up the house as a bed and breakfast out of financial necessity. But she says she kept the business running for 25 years...