Dr Bags is quite popular.... I go to their Plaza Sing outlet. Friendly service and the staff or manager there is knowledgeable. Have sent 2-3 bags there for cleaning, colour touch up and HP coating. So far, so good. Only thing is if you do HP coating (water proof)... the bag becomes more matte in colour. Take note that I havent brought very dirty bags there - just vintage or preloved bags I bought and wanted a proper cleaning.
Honest crafters I went to Plaza Sing too but I think they moved to City Hall. Sent for cleaning and mend of stitching on 2 bags - came back well done but I had to wait a month or more.
I find both shops trustworthy... but do note that bag cleaning services in general not so cheap.....