I also agree with Jennywren but then again how long would it take to learn the process? When I started printing mugs over 10 years ago it took me about a day to get the process learnt and to a quality that I am happy with and more importantly my customers.
Have to disagree with Logobear on a few things as well.
Yes you can sell 30 mugs and get the same profit, however that is selling to individuals and not bulk, that would mean 30 different customers a day and is a completely different market to bulk (or rather trade) selling. I am sure you have many repeat customers etc at a shop, but I only need 5-10 customers to keep me busy enough. I have no need to advertise and my website has not been touched since 1997!!!! (p.s. 10 times 30 is 300 not 200

)))
200 mugs a day is only 1 pallet a week so there isn't really any issue with receiving them, you can always set up a deal with your supplier of mugs to take one every week and delivered at XX time. Suppliers and couriers love that sort of thing as its easy to schedule. There is also the added benefit that stock control is a walk in the park with selling 1 item in bulk. No need for any other items like hundreds of garments in various colours and sizes sitting on the shelf for ages before anyone purchases.
Having said that, there are two different markets here and it all depends on your skill set which one you prefer and are better at. I remember having an email conversation with WorthDoingRight who prefers to "spread" his customers. I personally could not stand the thought of hundreds of customers with all the invoices, bills, PDQ receipts etc etc. It would also mean I would have to deal with the public which is something that makes my skin crawl

Don't get me wrong, I admire anyone who runs a shop for this sort of work and it is something that I personally would love to do, but I also know it would be a mitigating disaster as my skill set is completely wrong for that sort of business.
Lastly, I have heard that Supermarkets are bad payers and personally I wouldn't touch them. I was contacted recently by two different retailers about mugs, the price was right but they wanted 90 day credit terms. I refused and said that in the present market I would require 50% upfront and then 50% on 30 days. They refused, one of them has now gone into liquidation and I suspect the other one will have to restructure in some way or another.
To get back on topic, it is really down to what Dan is good at whether he ventures into bulk or into retail. he may well have a very good contact who has said if you can do it you can have it (maybe not even Asda). If I was in his shoe's I would look to farming the contract out to the likes of me and then adding 5p per mug for doing nothing, but then I might be biased there

USING: Whatever it takes to get the job done...