Sweetness1
Over a year ago I bought a book of 1st class stamps from the local newsagent mostly for birthday cards. A couple from the same book of 6 were counterfeit( I found out from recipients being asked to pay fee!) The others weren’t. I wouldn’t buy from my local newsagent now though.
Clearly if part of the book were classed as fake but not all, the detection system is unreliable. I use very few stamps these days and the ones I currently have were bought in order to send my Christmas cards. No problems so far but next year I shall only buy the Christmas special stamp books and buy from the post office. Most of the things I post are packages which I pay for at the post office and get one of their printed stickers put on. I assume they are safe. I always keep the receipts as they are usually for gifts sent to neices and nephews who live overseas.