I only give 'temporary receipts' out during the year and those are only for CASH payments and it says right on them 'temporary receipt ~ not for tax purposes' ... if they are paying by EMT or Cheque or what not they have a 'receipt' via their bank statements and canceled cheques!

At the end of the fiscal year and before the February 28th deadline they get one FORMAL receipt for use on their income taxes ... I have the practice that they sign that they received it and agree with the amount listed to avoid conflict. I keep one copy and they get a one for their records .... if they loose it they have to pay for a replacement and the replacement will say DUPLICATE on it so that they cannot try to use 'both' should they find the original!