Final answer:
Street musicians were indeed hired for outdoor garden parties, an activity with historical precedent and a practice consistent with entertainment norms.
Step-by-step explanation:
Throughout history, street musicians were indeed hired to play at various functions, including outdoor garden parties. Hiring musicians for entertainment dates back to ancient times and continues in various forms to this day. The practice of hiring musicians can be considered an externality as it benefits not only the direct participants in the exchange (the hirers and the musicians) but also potentially provides enjoyment or disturbance to others who are not part of the exchange, such as neighbors listening in from nearby properties. In the given context, references to the use of music at social gatherings and the presence of musicians in street settings suggest that hiring musicians for garden parties and other events was a conceivable practice.