We can help advise you on how many vouchers to give away but ultimately it's up to you. Sometimes if you are offering something very special then keep it minimal to keep that sense of exclusivity however as a general rule we think you should offer quite a few to encourage participation.
Once we have set the number of vouchers our system will automatically alert users when your vouchers are about to expire so that no one gets disappointed.
We also recommend that the voucher codes we work with limit users to one purchase, although we do like to see people sharing so we do encourage our users to share their vouchers. More vouchers out there more potential sales and more smiling faces.