I have just gone over the Market rules and under the "IV. Products" section, the first rule may be interpreted as being that Source Code cannot be supplied to the user:
The Product offered through the Market service can be provided only as a compiled file with the EX5/EX4 extension.
Is this really the case or am I interpreting it to rigorously?
As anyone else supplied Source Code to Buyers with MetaQuotes' consent?
Was it a one-time thing or is it a regular thing you do with your sales?
Logistically, how do you carry it out? For every sale, do you get the User's ID in order to send them the source code or do you use some other process?
I have only 1 product I offer the source for.
After purchase buyer must message me and give me his email but I guess you could use any messenger.
Since, I have never used the Market for sales, could you elaborate on what the "receipt" is like or how it is processed?
I have previously purchased a product on the Market and I don't remember receiving any "receipt"! All I have is a one-liner in my Profile's Purchases section informing me that I purchased (and the number of activations) a particular product, but there is no extra information that could be used by the seller to verify that purchase, nor did I receive any email confirming the purchase.
Benjamin Dixon: Yes, I asked for permission first, and it was a couple years ago that I was given permission. I have only 1 product I offer the source for. After purchase buyer must message me and give me his email but I guess you could use any messenger. Can not have multiple options/prices for a single product, must use two separate products i.e. one with src and one without. You must manually check his/her receipt to be sure.
A bit late, as I see you already got most answers from Benjamin...anyway :
1. Yes it's allowed but you will not be able to do it with the Market. You can't include the source code, you will need to send it separately.
2. The seller didn't receive any information about the buyer.
3. One product one price.
4. Yes and no. As the market is not done to sell source code, I will rather use freelance section, it's there for people ask custom coding. So you could advice on your product's page to contact you via Freelance section. Just an idea.