Do you take deposits?
In short: Only when the written scope says so, and the amount is stated there. Most work does not need one.
A deposit is sometimes stated in the scope for larger jobs, such as a multi-day collection appraisal or a run of breaks booked for specific dates. If one applies, you will see the amount and what it covers before you sign.
A deposit is part of my fee, never a holding of your money for someone else. I do not provide escrow or hold funds, and grading fees are always prepaid by you directly. See do you hold my money?.