hey vanhooglesnort, this is a touchy subject with many opinions and practices out there. My thought on this is if you want to spend all your time going thru peoples watches to give a diagnosis and not get the job you may be in the poor house soon 
. I have a hard time doing professional work and not getting paid a professional price, ssssssoooooo that then leaves us with, what is a professional price and for doing what???? I find this question difficult as I labor over it 
. I usually get caught up in the mister nice guy syndrome and worry about someones reaction to my pricing when in fact I am underpaying myself because I do much more for my customers and their clocks than most would…..if I take my car in for a diagnostic test it can cost me $80.00 😯 , or to have a plumber come over and unload a tool could cost me $75 😯 without anything being done. what I do do is spend time talking with the customer, free estimates without any dismantling, and then telling them the price for getting their clock running again (or pocket watch) and do the best professional, conscientious job I can!!!!, does a initial inspection always reveal all the problems that need to be addressed????? the answer is NO. for to do a superior job on a clock or watch there are things that cannot always be quickly seen and many things that can be checked and adjusted properly throughout, even though the initial inspection can reveal many obvious issues that need addressing, there are most likely issues that cannot. for instance a pivot on the front plate of a mantle clock may need replacing because someone in the past decided to solder on a hunk of sharp metal to hold it in place 🙄 , or a safety pin hiding behind a mainspring that was used to hold the count wheel on 🙄 , now you need to find a proper part. In a watch you are right when you say @vanhooglesnort wrote:
time consuming and difficult to diagnose
especially for a beginner like me . I usually will take a initial look at the works, check all that I can without taking it apart and having a set price for a service (which you have to determine for your customers), anything else would have to be extra, (new mainspring, cracked jewels, staff, ect…) I like to use the analogy of a old used car, to get it running again may cost more than what its worth and I have to weigh the pros and cons of junking it and getting another or fixing it, but if its a 69 camaro that your dad bought you when you graduated and its the car you met Hildagard in , then the cost doesn’t matter, a initial upfront “ESTIMATE” will prepare me, and is usually not close to the final bill. Still the mechanic needs to dig into it to find out why it is hissing, spitting and sputtering and it is most likely not the air in the tires, filling the windshield washer fluid, or dumping more oil into the engine till its flowing out of the fill tube (kind of like alot of people think with their clock, add oil and it will run). Show me the mechanic that will disassemble your engine to tell you exactly whats wrong, with the chance that he may not even get the job!!!! Well maybe I opened a can of worms, this pricing thing IS difficult, my grandma said to me once, “pay yourself what your worth, and be happy” my grandpa said, “who knows how the cookie will crumble”, well I didnt always listen 🙄 and if what grandpa says doesn’t make much sense it is because its not supposed to . I dont know if I even answered your question but remember this, if you are serious and stand behind your work, you have probably invested alot of time and money into it, your name as a clock and watch repairman is at stake, dont let someone take advantage of that. William