The biggest mistake a competitor can make is thinking Salesforce is a CRM. They may sell themselves as one, but that is just to get a foothold in a company's sales system. Salesforce actually sells (1) an ecosystem that lets your company connect to any other software out there and (2) a platform on which you can build...basically anything. These two together ensure that every one of their customers is 100% locked in…
Fortunately there is a whole field of business devoted to this problem: go-to-market strategy. Target a niche, offer a compatible product, offer a significantly better product, offer a different product, offer a cheaper product ... the options are endless.