Email is preferred because messages can be saved to create a history of the project. This is particularly useful to me if I need to refresh my memory about one of your preferences for your project.
I live in rural Oregon. Mail service is dependable but not as fast as in urban areas. I receive mail at a mailbox cluster that is several miles from the Post Office. Since it is a two mile drive to check the mail I don't do it every day particularly when the weather is bad. Incoming packages may be too large for the boxes at the cluster, requiring me to drive to town to pick them up once I have received the pickup notice at the cluster. Conversly outgoing packages are driven to town to be mailed. Outgoing mail takes up to two overnight hops before it arrives at a distribution center. All this means that your expectations for mail to or from me should be adjusted to take up to three days longer than what you may be accustomed.
Most of the models that are bought and sold nowadays are used models. If such a model is in poor condition with hidden flaws, some sellers may either conceal that, or if they don't understand the model sufficiently or inspect it to see flaws, may not be aware of the flaws. That model may be purchased by someone who was not aware of the flaws. Outside the realm of flaws, some models are either not worth working on, or are of such construction quality, that working on them can be very expensive.
Fortunately those models are not common but they do exist.
If you aren't sure about your model you should always have a conversation with me about it.
I want you to be aware of the possibility that your model may be a difficult project.
I have learned over 30+ years of working on model locomotives is that most jobs are are simple and straight forward, and some can be a mess.
A models may have severe hidden problems that won't become apparent until they are disassembled and work on them has been started. By that time you and I have invested in the project, and the decision on whether to continue must be made.
For example, here are some examples of the spectrum of things I have bumped into.