The short answer
A good reply feels like help from a person who understands the thread. Avoid generic praise, fake familiarity, irrelevant links, and mass-produced language.
Answer
How do I write cold replies without sounding spammy?
Write cold replies by proving you read the context, naming the specific problem, offering one useful idea, and making the product mention optional rather than forcing a pitch.
How Wally helps
Wally drafts replies from the actual conversation and product context, then lets the user review and approve so the final answer can stay accurate and human.