1- meh, depends on what you’re offering. Delivering on time should be enough. I have clients that would be pissed off if they got it too quickly (“What, I paid you that much for something that took you a few hours to do???”).
2 - This helps. Quality is more important than speed though.
3 - This does not make sense. Buyers are clients. Clients are buyers. Same thing.
4 - This is by far the best tip imo. Learn to read the buyer/client. This can help with a lot of things - minimize bad reviews and cancelations from nightmare buyers, pricing, expectation management, etc. There are certain profiles that are an instant no for me - I know we won’t be a good fit, and not worth my time (or theirs).