Most shops that ask for a deposit are completely legitimate. A short checklist protects you on the rare occasion one isn't.
Deposits are normal for special-order parts or jobs that take a shop's bay out of rotation for multiple days. They're worth a quick check before you pay, not because most shops are dishonest, but because the check itself takes thirty seconds.
A legitimate deposit is usually tied to a specific part being ordered on your behalf, or a scheduled multi-day job. "General booking fee" with no specifics is less common and worth a follow-up question.
A text message confirming the amount, what it covers, and that it's deducted from the final bill is enough. You're not asking for a contract — just a paper trail.
Ask what happens if the part is wrong, delayed, or you change your mind before work starts. A shop's answer to this question tells you more about how they'll treat you than the deposit amount itself.
Card payments give you a dispute path if something goes wrong later. This one is less about the shop's honesty and more about keeping your own options open.