But on Wednesday he encountered a first - a stash of jewellery hidden in a hollowed-out book.
It was pure chance he found the jewellery, which included a cameo brooch, a ring and an earring, he said yesterday.
"When I opened it, the jewellery fell out. There was one earring in there and I thought there must be a matching pair, so I hunted around and found the other one in the bottom of the box," he said.
Mr Hamblyn returned the jewellery and book to the Dunedin family which had sold him six cartons of books, receiving grateful thanks and a bottle of wine.
"They said had been looking for the jewellery for years. They knew it existed but didn't know where it had gone."
The family did not want to be identified or interviewed.
Mr Hamblyn, a former librarian who with his wife, Cheryl, has run the Read On! bookshop in the Gardens Shopping Mall for almost seven years, said he checked the larger books in the other cartons from the family but found no more surprises.
Banknotes, photographs and strips of negatives were common finds, he said.
On one occasion he was able to return to relatives letters, photographs and diaries which he found in a box of books sold to him after their owner's death.
"It was heartbreaking to think that history was almost lost to the family."
Mr Hamblyn said he once almost sold some of his own money with a book.
He had hidden the shop's float in its pages but forgot to retrieve the notes.
It was discovered some time later by his wife while she was flicking through the book just before selling it to a customer.
He said had learned his lesson and now kept the float in a safe rather than in a book.
