Decent Behaviour?

I've not done many commissions but have had no trouble until now. I realise that I've been a bit stupidly trusting here but wonder what you think.

I did a house interior shoot involving hundreds of images for HDR composition and internal panoramas. From these I worked up a range of shots for the customer (a rental holiday property owner) and put them up in a little private gallery for their approval and to choose which/how many they wanted to use. I was preparing an invoice today ( a week after putting them up for approval) and needed the address so I went to their website only to find they have already lifted all the images from my website and installed them on their website. Foolishly I had not watermarked them though they are only 800x600.

Am I the only one who thinks this is poor behaviour, even if they ultimately pay up? I have no reason at the moment to believe that they won't but this, and the fact that the owner resides in Hong Kong is beginning to give me sinking feelings.
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Brian
Fine Art Print sales of the Isle of Skye at:
http://www.eyeofskye.co.uk/