Official access and number safety
Start here, because nothing else matters if your number is restricted. Ask each vendor to confirm in writing that they operate on official platform access, and to describe the onboarding sequence: business verification, display name approval, and, if you are moving an existing number, how the migration works. Ask what happens if a display name is rejected. Vendors who handle this well will have a clear document ready, because they answer the question every week.
Template workflow
Submit three genuine templates during your trial, including one marketing message and one containing variables. Record how long approval took, how clearly a rejection was explained, whether the interface helped you correct and resubmit, and whether categories were assigned sensibly. This single exercise separates tools more reliably than any feature list, because template friction is what stops campaigns from shipping on the day you planned them.
Inbox behaviour under load
Any tool looks calm with four conversations open. Test it with two agents and a realistic morning. Check assignment and claiming, what happens when two people open the same chat, whether internal notes and customer history are visible without switching screens, whether search finds a thread from three months ago by number or keyword, and what happens to an agent's conversations when they leave the company. Continuity matters: conversation history should belong to the business rather than to a person.
The link to pipeline
This is where the category divides. Ask whether an incoming message creates or updates a lead record, whether that record carries a stage, an owner, a next action and a source, and whether the thread appears on the record alongside calls and emails. Test it by running one genuine enquiry all the way from first message to closed deal and then checking whether the pipeline report reflects what happened. If the conversation and the deal live in separate places, you will be reconciling them by hand forever.
Automation you can build yourself
Write down the one automated flow you actually need, most often an away-hours acknowledgement that captures a name and a requirement and creates a task for the morning. Then build it yourself in each trial. Building it teaches you about the builder, the documentation and the limits in a way that watching a polished example never will, and it tells you whether the flows you want later will be within reach.
Cost modelling
Estimate your monthly conversation volume split by category, then ask each vendor for a written worked example bill at that volume with software and platform charges itemised separately. Ask what happens when you exceed the estimate and whether anything stops. A vendor who produces that document quickly is easy to work with; one who deflects the question is telling you how the invoices will feel.