The biggest red flags when hiring a designer are vague quotes, no local portfolio, big upfront deposits, and same-day signing pressure. Add a quote given without ever walking your property, and no proof of license or insurance where your state requires it.
A fair process looks like this: a site visit, a written scope with materials and a timeline, references you can actually call, and staged payments tied to milestones. Deposits above 30 to 50 percent are unusual for residential work. Full design fees typically run $2,000 to $7,000 in the US, so vagueness about what you get is expensive.
It also helps to arrive knowing what you want. Generating a few concepts of your own yard first costs less than one consultation; see OutdoorBrite's plans and pricing.