did he show his workpermit too?

We always travel with business visa, not tourist visa. If working permit is needed, we will also get the working permit.

Most of our client doesn't want their contractor come illegally, they said it is not compliance.

A Business Visa does not allow you to import multiple laptops without the correct paperwork. I have been stopped by Thai Customs and when I explained my need for multiple electronic items I was asked to place a bond for them, refundable once I left the country (the bond was arranged by an agent employed by the company I was visiting). Yes I imagine 99% of the time you can get away with it but it doesn't mean that it is legal.

As there is now no duty on laptops (though they are subject to 7% gst I cannot see how computers are much problem.

One does have to wonder why the OP is bringing in so much clothes and in the original packaging too. Clothes are one of the few things that can still be had at a reasonably cheap price here.

Rule #1 when traveling, ALWAYS remove items from their original packaging.

My #1 rule is to bring my passport.

Reminds me of a time I was inspected at Heathrow, after telling them i had arrived from Thailand they asked if I had any counterfeits.. I said you'd better get a paper suit for me as nearly every clothing item in this case is some sort of knock-off... They looked and laughed at my dirty shirts etc.. and sent me on my way..