For anything still in production (in the exact same form), they can eff right off.
For vintage, discontinued or restored equipment, then they're absolutely within their rights to ask for their costs - that could still be lower than a buyer would have to pay elsewhere.
Unfortunately, for something someone has "only had for a week or two", you only have their word for that, and just like how new cars collapse in value as soon as you drive them home, buyers will always be wondering "perhaps this is for sale so soon because it's actually faulty".