Examine at the counter
With the customer watching.
Heat-fixed, oxidised, or six months old. The fabric is the limit, not the effort.
Customers are rarely told no at a dry cleaning counter, which is why so many collections end in disappointment. Set stains, heat-fixed marks, dye transfer and oxidised sugar are frequently permanent, and the honest version of the service is saying that before taking the money rather than after three attempts that thin the fabric.
The care label is the other place where agreeing with the customer does harm. Labels reflect what the cloth, the interlining and the trims will survive, and a garment washed against its label commonly comes back shrunk or distorted. Doing it only on a written request keeps the decision where it belongs.
The limit worth knowing in advance is liability. Across the trade, compensation is based on an item's depreciated value rather than its replacement cost, which surprises people holding a two-year-old coat. Declaring something exceptional at the counter lets cover be discussed while there is still a choice.
With the customer watching.
Otherwise at the owner's written risk.
Before taking the money.
Bring it in. The advice at the counter costs nothing.