Taking deposit and first months rent

I can’t quite believe that I am asking what is the fairest way of taking the first month’s rent and deposit, as it seems so simple, but here goes. 

Some tenants moved into my very nice flat last week, having only paid a holding fee (normally about a third of the rent), for which I emailed receipt (I suppose I could have been anybody with a key pretending to be the landlord).

When they arrived to move in and sign the contract they had not made a transfer into my account – which is normally what happens.

I reluctantly handed over the keys and had to trust them to do it later that day as they pointed out that it states in the contract that they will pay upon signing that document.

Well how do they pay upon signing that document?

They didn’t actually do it until the next day, so although all is well, it occured to me that I had been in a very vulnerable position for that 24 hours.

I know the NLA advise never to hand over keys unless everything has been paid; i.e. presumably in advance, although their AST states upon signature.

Conversely, when they pay into a landlord’s account in advance they are vulnerable – particularly if they are being duped by a scam.

Years ago cheques were normally used, but now I suppose one could take along a tablet of some sort and have them carry out an electronic transfer in front of you – seems a bit extreme though (unless they offer, which one tenant did recently).

What do you all do?

Thanks

Gilly