Like all SaaS products, CRM solutions run the gamut from lightweight services intended for quick and easy customer relationship and lead management, to powerhouse systems with integrated e-commerce solutions and advanced analytics.
While many small business owners worry that they'll sign up for a product that doesn't offer enough functionality down the road, these concerns are often overblown. Tiers of service and add-on features are nearly always available, and while more may seem inherently better, in terms of features and functionality, too many options within a system can be overwhelming, make the implementation process longer and more complicated, and cost more than necessary.
The best way to determine the features you require in a CRM is to list out, in layman's terms, what you want to be able to do. Do you want to have workflows with multi-level approvals built-in? Do you want to be able to email clients directly from your CRM? Do you have a team of in-house developers who are going to build out your system for you, and therefore need an open API? Whatever your needs are, list them out.
Make sure you also list any integrations you want to use (including proprietary legacy software, if applicable) and be sure to inquire about how such integrations are achieved. In some CRM systems, integrating with an outside solution is as simple as clicking a few boxes; in others you have to use a third-party tool (like Zapier) to click your way through the integration, and in others still you have to do actual hands on coding to make integrations happen.
By outlining your needs ahead of time, you stand a much better chance of getting a product that does what you need without overpaying for features you'll never use. It's also good to keep in mind that you can always upgrade – a company is never going to refuse to sell you more features in the future, so start addressing your most pressing needs first, and go from there.