How would handle a problem when a customer returns a product without prof of payment?

Do not make judgment merely upon proof of payments. Actively hear about the customer pain areas. As unsatisfied customers are the great way for business services/product improvements. Facilitate your client through state of art customer handling skills while guiding him about the way arounds. Tell him about the policies/procedures/ SOP's while keeping in mind the customer integrity. if somehow your client still don't understand your company's procedures/policies/SOP's. Give him a smile, and tell him in a professional way that he will consult his case with the management. 

Without proof? that's a big one, however the best bet would be to stick to the company policy on return of sold goods.

asses the legitimacy of his or her complain and asses the product returned and make sure the complain on the product is true n the product is in properer condition then take it from there in a respectable and understandable way

i will ask him to explain way he did pay the product , what is the method ( online, cash , credit , etc... ) ill go through payments through the day customer informed , if found ill submit the prof and compensate him , if not found ill inform the billing department for this mistake which mostly is online payments , if by bank ill ask him to recheck with bank , ill check my gateway company and see if there is any not issued payments. within this time i usually issue a free service for customer if he have a payments history if not founded ill explain very carefully that i havent found any payment as described by him. 

first of all if he return the product means that he never realize wath the product made it for it,,so even if show the proof of payment doesnt mean nothing,  Personally i will return his money and more people going to pass to buy my guarantee product,,,

I would make the conversation in a calm tone and :

1.ask for an ID, if he/she could remember the date of purchase then the better

2.. check if it is within the warranty period

3.counter check the product specification of the item bought to that of the product being returned

4.check the product for any damages, unless the damage is a manufacturer's defect

5. accept the product being returned if it met all the above criteria,if it was not met then ask what the management management would say about the matter.

6. after everything was done than say 'thank you, have a good day'

First of all don't make judgment  about proof of payments. Hear about the customer problem carefully and provide facility to your customer through the art of customer handling skills while guiding him about the way around. Guide him about the policies/procedures/ SOP's while keeping in mind the customer integrity. if somehow your customer still don't understand your company's procedures/policies/SOP's. Give him a smile, and tell him in a professional way that he will consult his case with the management. Unsatisfied customers are the great way for improving the business and services/product of the company.

I will consider first the companys policy  that customer will be the first to consider but in a rightful manner of communicating, try to  meet their demands and providing them the best service your company can be.courtesy is very important. Because customers always go where they are treated well.When the value isnt obvious or when the level of service slips, the customers slip s away.

This is a reoccurring issue in many stores. Like stated above, do not be haste in making a decision. First actively listen to what the customer has to say. Examine the product and make sure it hasnt been tampered with, also make sure that your store actually carries that item! 

After listening to what a customer has to say, offer them to exchange the product for the same one or something of similar price. If worse comes to worse, give the client a refund. (This should be the last option)

Communicating with your client is the most important factor in this situation. If you seem like you are judging the client or doubt the client in anyway, they will become defensive.

Use words like "I understand your situation" or "I can see how that would upset you..." etc.

Finally make sure to end on a good and positive note whenever possible.

I will as the customer when he exact date and time upon buying so that I can retrive the pos sales.

firstly as a sales person, one would need to recognise the customer and code in their complaint about the product. Secondly i would ask the customer to provide information about were they bought the product and call in the store so that they can retrieve a purchase document that has correct specifications as given by the customer.