Isaac owns a shop selling fishing supplies. He places an advert in his shop window, "Five handmade fishing rods for sale: each 1,000. Available only to the first five people who pay me this amount by Saturday 1 May". In his window he also displays a box containing ten fishing knives. The box has a sticker on it which reads, "Handmade knives - 200 each".Devi sends Isaac 1,000 in the post on Tuesday 27 April and says she will collect the rod on Monday 3 May. The letter gets lost in the post. On Thursday 29 April Charles telephones Isaac and asks if he can buy two rods for 1,500. Isaac says he wants to think about Charles' offer. Later that day, Isaac telephones Charles and leaves a message saying "I am happy to sell you two rods but the price must be 1,700". On 30 April when Isaac does not hear from Charles or receive any other offers for the rods, he places a notice in his shop window stating that the handmade rods have been withdrawn from sale. On 1 May Charles goes to Isaac's shop with 1,700. He is in a rush and so does not read the notice in the window and asks for two rods for 1,700, which Isaac declines. Charles says, "Okay, I'll give you the 2,000" but Isaac explains the rods are no longer for sale and points to the notice in his window. At the same time, Bronwin enters the shop to buy a knife. Isaac explains that he now realises that it was illegal to sell the kind of knives he has in his window and so refuses to sell one to Bronwin. Advise Isaac.