I have a question about the fair use of vouchers.
The facts are as follows: At a lottery retailer, a lottery ticket was purchased (valid for 4 consecutive weeks, for the same 6 fields [with 6 numbers chosen from 1–49 per field] ). The cost of € 29.5 for this ticket was borne by person 1, who had requested the lottery ticket. However, instead of using the selected numbers, the sales clerk let the computer select entries randomly (for 4 weeks and 6 fields).
The mistake was noticed when the winning numbers of the first week were announced. Each week the 6 winning numbers in the lottery are announced. There were no wins for neither the requested nor the issued lottery tickets in said first week.
To compensate for the error, the lottery company sent two vouchers good only for lottery costs each with value V= €5. This was out of courtesy, legally the buyer of the ticket is responsible for checking correctness immediately.
Before the vouchers arrived, a new lottery ticket was purchased by person 2 with choices as originally intended by person 1. This new lottery ticket was then given to person 1. Meanwhile, person 2 took possession of the incorrectly completed lottery ticket from person 1 with the agreement between person 1 and person 2 to keep any winnings on this ticket (3 weeks then remaining). Person 2 would otherwise not have bought a lottery ticket.
The expected value of a win for one field in the lottery is about € 0.4970268 (minus the cost of buying one such field on the ticket, which is about € 1.229167 ≈ € 29.5/(4*6), see above).
Question: What would be the fair use of the vouchers (to be spent on future lotteries)? And are there several approaches to what is fair?
I am only interested in how to approach the fairness question mathematically. Also I feel that one could disagree on what is fair and that is my main question of interest. Legal and monetary aspects are not of interest. I have supplied numbers because of a comment that the facts are hard to follow.
(Note to self, given the misunderstandings: Don't rely on computer translations, rather go with your own rudimentary knowledge of English.)