When should a startup consider buying a commercial solution instead of building one? It makes sense to buy when the problem being faced doesn't directly tie closely to the core value proposition, or when existing solutions aren't specific enough to meet the company's needs. On the other hand, startups should build their own solutions when the problem is closely tied to their core value proposition and there isn't a suitable commercial solution available that meets their unique requirements. In Zapier's case, they built their live chat and drip campaign tools because these were complex problems that required custom solutions to meet their specific needs, such as supporting diverse user bases and providing control over email campaigns. Ultimately, the decision to build or buy depends on the individual company's circumstances and should be made after careful consideration of both options.