To be fair, I think the SA is worried about bed bugs, which have become a huge problem in the US and, last I heard, are an increasing problem here. Their worry may be misplaced and even such a worry doesn't excuse rudeness; the person who spoke to nanapug could have explained politely.
Very hot laundry washes kill them but most people don't do very hot washes any more.
Fairness on the subject of bed bugs aside, I'm rather disgruntled with charity shops nowadays too, partly because they seem too showy and expensive, but also because I'm disgruntled with many of the large charities for other reasons. They have suffered from too much corporate creep in recent years.