As noted, the common wisdom is to buy used. However, when we went looking for used, we quickly discovered that 10 year old models were more than half the cost of brand new. To clarify, the particular manufacturer, model, and floor plan we wanted would have to be over 10 years old in order to save half the cost of a new one. With the new one, there have been several improvements over the years, such as pre-wired for satellite, LED televisions, electric water heater, and lighting fixtures. Additionally, by purchasing a new unit, we got to choose the colors and patterns of the upholstery. So there are times when sense (at least to me).
As to quality - you have really got to look closely and do a lot of comparing before you begin to see differences in quality. The carpet in one may look identical to another, but be a much lighter weight. Or the subfloor might be OSB instead of tongue and groove plywood.
Here's one for you: the cabinets in our camper are described as "glued and screwed" and "real wood" by the salesman. This would mean there are no staples holding them together. Pretty good deal, right? The documentation says the "solid wood core" is glued and screwed on all cabinet facings. Now what the heck does that mean? And is it still a higher quality than the camper that has staples holding everything together?
Shopping for a camper is a learning experience. There are some things that seem to be industry standards that you can't do anything about. There are others that will leave you wondering "what were they thinking?". The more you know, the better you will be able to define what quality means to you, what trade-offs you are willing to make to reduce weight and/or cost.
Good luck, and study hard!
