What is the ruling on working in the sale of iron pipes whose thickness is less than what is advertised, knowing that customers overlook this, and is it obligatory to inform them of that, given that leaving the job or changing its nature is currently difficult?

It is not permissible to sell a flawed commodity to someone who is unaware of its defect without disclosing it, because that constitutes forbidden deception and fraud. The Prophet, peace and blessings be upon him, said: "Whoever deceives us is not one of us," and "If they are truthful and make clear, they will be blessed in their transaction, and if they conceal and lie, the blessing of their transaction will be erased." As for selling it to someone who knows its condition and accepts it, there is no harm in that, unless it is highly probable that he will use it to deceive others.