It could be a car-wash that scratches your vehicle or a window cleaner that breaks your windscreen. I'm sure it happened to many of you. But in my case it's a laundry that makes huge holes in entrusted duvet-cover, packs it nicely as if nothing happened and charges me the full bill. When I later discover the damage and go back to confront them they blame it on my linen or chemicals they used but in any way deny any responsibility or refund. This happened to me at several laundries and each time I moved elsewhere. But loosing 1000 THB each time this happens plus paying their bill for cleaning of damaged item doesn't seem to be fair. Each time the laundry seems happy not to have our business any more as long as they don't need to pay for the damage. So what do Thais do in cases like this? Grab a few muscular guys with Big Sticks and go talk sense to the culprits or what?

huge hole in the duvet cover?

can you identify the cause? Chemical damage looks different from mechanical damage or a tear. Chemical damage weakens all the fibres around the affected area.

How can they deny responsibility if the damage is caused by their chemicals/machine?

I would move on and find another laundry, perhaps find a DIY laundrymat or have someone recommend one in your area?

Getting heavy wont work, imo

Unfortunately, that happens a lot. I remember a pair of trousers I had dry cleaned in New York. Part of an expensive suit, but only needed the pants touched up a bit after a mess at a biz lunch. They came back a slightly different color and for sure a different feel. Went back to them and they said "hey, sometimes that happens".

I had a laundry service in Bangkok lose some of my really expensive trekking clothes. Wool socks, quick wicking Ts and undies, etc. Reimbursed me about 1500B. Maybe 1/5th of the actual cost, but hey...I got something back...