Any experiences out there with mountain bike brakes that will not stop squealing?

Have tried pad replace x 3, swapped disks, did all combinations of those. Wheels seem true, asked them to check and the spoke tension etc, but I am going off hits on the net For info, I do not have the background.

Any suggestions welcome. Next step with mechanic I have is a set of Avid BB7 to replace the Shimano Deore that are on there . I will do almost anything now as the bike is useless, you cannot ride it. Popping around bkk today for experts who may have an opinion, let me know if you know w good shop.

I go to a guy at fortune tower and he looks to me to run a great shop.

Thanks in advance

Youtube has some how to vids for squealy bike breaks.

Yes thanks I have seen them and mention them at these shops, three in total so far. Hoping they know and do the whole drill, but maybe not. I do not the space time or tools to even try so hoping the shops do

Cherrs