Wait what? Don't plumbers and Carpenters have their rates on their website or they can give you a quote over the phone? You dictate the price?
Most of them have no website. For real big jobs you receive an estimate of the cost.
Minimum hourly rates are $72 an hour for the lowest qualifications. So you pay quickly over $100 for a decent qualified worker.
I don't dictate any price, I hire them. In general these people have so much work that you have to wait weeks before they can come. So if you are difficult they just refuse you, as they have more job to do than time.
As for the cleaning ladies, in the US they usually work for a company and that company has it's own rates. You just need to tip them when they're done.
We don't tip, by law all prices are ALL INCLUDED. The companies that send you these cleaning women are so desperate that they offer a company car for each cleaner they can catch. The demand for cleaners is much bigger than the offer. If you want one now you go on the waiting list till they can find a cleaner. Can take months before you will have one. Rates are never below $15.