I've been happy with Charles Ro the last couple of years, but I ran into a problem last year and I had to scramble to find one of the Lionel made in the USA cars that were shorted due to the manufacturer bankruptcy (ended up getting it from Nassua Hobbies).
This problem only pertains to small orders, so it won't effect too many folks on the forum.
If you have multiple items on order, and the total of the items that have arrived in stock is less than $75, than Ro doesn't ship until other items on your order arrive and the total goes over $75. If one of the items goes out of stock while your order is in this pending mode, than you are out of luck. They don't set the items aside for you. It isn't a real common situation and normally isn't a problem as there generally aren't fast sell outs of the less expensive (under $75) items, but it can happen.
There is a way to avoid this potential pitfall. When you place your order, request that they ship items as they arrive. This could end up costing you more money for shipping, depending on when items arrive from the manufacturer, but you don't have to worry about items going out of stock.
I'll probably continue to order from Charles Ro.