A LHS has the problem that maintaining an inventory and a store adds to overhead cost. Let's face it, in today's world, items are bought on the basis of price alone. I'll be honest: that's how I buy, subject to the exception that if the would-be seller has a lack of integrity, or demands I agree to arbitration in South Podunk (as one model train seller does), I won't deal with him/her
One aid might be to have a crackerjack tech--not merely one who has attended a training course, but one who really knows the details. While this wouldn't have an appeal to me, it might to other buyers.
Personally, I wouldn't want to invest my money in opening a train store. Too much cutthroat competition for what is essentially a surplus-money market.