The auditor performs the independent examination and issues the report. An advisor can help you define scope, identify gaps, and improve processes. Software can organize work and collect certain evidence. Your management team still owns the system, controls, and decisions. Before buying a package, put those responsibilities in writing: who writes drafts, who approves controls, who fixes gaps, and who answers audit requests? Also identify the actual CPA firm issuing the report. A bundled service can be convenient, but the product name on a sales proposal is not enough to establish who is doing the audit.
Related: SOC 2 audit and compliance hub.
Further reading: AICPA SOC resources; AICPA ethics: SOC tool-provider arrangements.