I'm pretty certain you can use a voucher code from Amazon on any account you'd like - so the client could send the voucher to themselves and then just text you the code, but I don't know if that would get around the problem highlighted above with finding out the name of the sender.

I very strongly suspect that the person who applies the code to (one of) their accounts will see the name of the original purchaser, if Amazon know it.

Buying them via a shop would restore the anonymity, but you can only get specific denominations that way.

I've asked for an Amazon voucher as payment for a deposit and the client has sent me the voucher code. Is this secure? I don't know the client, not met him before so don't want him pulling a fast one and cancelling it or reporting it stolen after meeting.

Add it to your gift voucher balance and spend it ASAP, you should be fine...plus you will instantly see if the voucher code is genuine.