What kind of proof did the man probably have when he bought the radio?

M:Good morning,Miss. I’d like to speak to the manager.
W:I am the raanager,Sir. How can I help you?
M:Oh,really? It’s this radio. It doesn’t work.
W:Mm... did you buy it here?
M:What do you mean? Of course I bought it here. Look,you switch it on and nothing happens.
W:Could I see your receipt?
M:Receipt? I haven’t got one.
W:Oh, you should have got a receipt when you bought it.
M:I perhaps did. I must have thrown it away.
W: Ah, well, have you got any other proof of purchase, the guarantee, for example?
M:No. It must have been in the box. I threw that away,too.
W: Oh,dear. You really ought to have kept it. We need to know the exact date of purchase.
M:What? I only bought ityesterday! That young man over there served me. Oh,I paid by cheque. I’ve got the cheque stub.
W:That’s all right then. Did you check the radio before you left the shop?
M:Check it? No,it was in the box. I hoped it would work. It wasn’t a cheap radio. It’s a good make.
W:You should have checked it.
M:Come on! Do not tell me what I should have done, and do something! Either give me my money back or give me another raido.
W:There’s no need to get aggressive,Sir. Let me look at it... mm... you see this little switch on the back?
M:Yes?
W:It’s on" main", and it should be Oh"battery". You really should have read the instructions.
M:Oh!