re: Becoming a professional woodworking or not

Like you, I’m sure, we have been doing this a long time and have a pretty good idea how much something should sell for.
I evaluate cost several different ways and usually take an average of all the numbers.

Look at the job and plug in a price off the top of your head at what you think it should sell for. Also try to think what it would cost if someone else was doing it.
Figure material, labor and overhead and get that number.
Break the project into different parts and plug in a price for each part and see where you come out at.
Figure a per foot price and see what it is.
I usually estimate my time going per day, or on bigger jobs, per week.
Plugging in numbers in all of these different ways will show you what numbers don’t look right and should let you zero in on where you need to be.
Of course, I take advantage of my clients wealth if possible, but not to the point where it’s criminal.
Always be fair for the service you provide. My reputation allows me to charge at the upper end of the scale because all of my work comes from referrals by satisfied clients. Learn a drawing program so you can show your client exactly what they are going to get. This alone will help sell a job.
A client will be glad to pay more when they have the confidence that the work is going to be top quality, including covering floors and cleaning the job site of your debris daily. Don’t ever let the client clean your mess.

Last of all, I think this is the most important thing to build you career.
Always be up front and honest with your clients, even when it’s not in your favor,
this will go a long way for your reputation.

Anyway these are some of the tips that have worked for me along my 35 years or so of being in business for myself.