You will spend more time with your implementation partner than with the software vendor, and the partner will make more of the decisions that affect the outcome. Most selection processes still spend ninety percent of the effort on the product.
A few questions separate partners quickly.
Ask who is actually doing the work
The people in the sales meeting are frequently not the people on the project. Ask for names, ask what else those people are staffed on that quarter, and ask who replaces them if someone leaves. A partner who answers that comfortably has thought about it before you asked.
Ask them to describe a project that went badly
Everyone has one. The useful signal is not the failure — it is whether they can describe their own contribution to it. A partner who narrates a difficult project entirely as the client's fault will narrate yours the same way.
Watch how they handle your requirements
If they agree to build everything you describe, that is not service — it is a quotation strategy. A good partner will push back on at least some of your requirements, and will be able to explain when adopting a standard process beats reproducing your current one.
Check what happens after go-live
Implementation ends; the system does not. Ask what support looks like in month three: who answers, how quickly, and what it costs. Ask how they handle the annual version upgrade. If the contract is vague there, the relationship will be too.
Look for domain fit, not just certification
Partner tier and certifications tell you a company met a vendor's criteria. They do not tell you whether anyone there has implemented in your sector. Ask for a reference in a business shaped like yours — same size, same constraints — and actually call it.
Price belongs in the decision, but it is the least predictive part of it. The gap between a good implementation and a poor one is measured in years of usable system, not in the difference between two proposals.
Whoever you choose, the questions above cost nothing to ask — and the answers are usually clear within a single meeting.