Like everything else here, you cannot rely completely on what others say or do. You need to be actively involved and repeatedly demonstrate that you will followup and you will check their work and you will verify what you are being told. It needs to be clear that you will catch on to anything hinky sooner as opposed to later.
Don't pay for everything up front. Final payment is always conditional on an acceptable result. Even with the trades, it is important to get your workers invested in your project by having some of their capital committed alongside yours. If I am asked to fund the purchase of materials for a job, I advance only half and pay the other half when those materials are used up or the project advances to the next stage and more stuff is needed. If my contractor can't afford their share or is unwilling to go 50/50 temporarily, I find someone else.
Lawyers, sometimes, you have to hire another one to check the work done by the first one if you are suspicious. Check that paperwork has been filed. Ask for file reference numbers and receipts for payments to govt departments or the payment of fines/fees. Stipulate up front how often you expect your lawyer to followup with you to report progress. Make it clear that you are only prepared to wait 24 hours for replies to inquiries or emails. You are the client, you are paying the bills, it's all about you. If your lawyer doesn't get that or doesn't care, it's up to you to make a change and make sure they know why.
Doctors are the same. You have to talk to them, ask questions and be satisfied with their answers after doing your best to ascertain that what you are being told is in fact the case. Second opinions here like at home are a necessity. These professionals aren't gods to be worshiped and tiptoes around. They are people who can and do make mistakes. In the end, it's you who has the final say what happens to you.