When repairing laptops, I tell my customers not to bring it in unless they are prepared to throw it away. I also will not order parts, except parts with access panels, until I have the machine disassembled. I would not want to spend $300.00 on a new screen and then break the bezels or crack a circuit board while taking it apart. After disassembly, I then quote them a price for repair. I don't charge them for the labor if they choose not to repair it. I consider it practice, since they are so damn hard to get apart.
If they're your customers - meaning that you're doing it as a business, as opposed to just trying to help out a friend or relative gratis - I'd think that any parts that you break during the procedure would be on your
nickel. (Actually, I'd expect that even if it was "only" a favor for a friend.) It'd be like if I came into your home to prep the walls in your dining room and prime/paint the ceiling and walls... and, while I was there, I knocked a hole in one of the walls, looked at it, and said, "Gee, that's tough, Fred. Well, I'll just be going now." Some folks would get a mite bent out of shape if that happened - I'd be one of them.
Regardless, I wanted to post that whenever someone does at least a partial disassembly on a laptop that is more than a few months old, they should (IMO) take the time to clean the air path, heat pipes, fans, and heat sinks. This can extend the life of the laptop, stop "instability gremlins/shutdowns, and even help performance if the CPU is one that can be throttled (a laptop that is running hot will often be unable to maintain its higher CPU settings). Unfortunately, in some (many?) laptops, doing this can require quite a bit of work; sometimes the last bit that you come to is the fan/heatpipe assembly. Also, it doesn't hurt to consider removing the old thermal grease/tape that you find and replacing it with new. After all, it'd be regrettable if one were to put time/parts/labor/money into repairing/upgrading a laptop only to have it fail due to heat at some point in the future.
BtW, it can be helpful to snap pictures along the way with a digital camera (or the equivalent on a cell phone), make a video, or even keep a running commentary going whilst making an audio record. Then, when you are reassembling, if you have any uncertainty along the way, you can refer to your audio/video/notes/etc.