There are not really standard wholesale prices for used vehicles, especially for RVs. Market prices vary seasonally, regionally, even locally, and in most places the RV market is not large enough for sale price surveys to produce usable information. Thus "blue book" prices for RVs tend to be estimates using depreciation tables against MSRPs when new.
A dealer might have lees than 1/2 his asking price tied up in a used unit, or more than 80%, depending on how and why he bought it. Or what is on a dealer's lot might be a consignment, and the seller needs to get enough money to not be selling it for less than he owes, which might be a lot more than a reasonable market value.
This gets worse as RVs get older, depreciated values go way down, and condition becomes more important than prices from depreciation tables. Thus an old motorhome might be $10,000 in the book, a seller with one in excellent condition with recent upgrades or important maintenance (just put $2000 into new tires) is going to want more, but an estate just wanting to get rid of one in good condition might sell for $5000 or less. A camping buddy just recently picked up a $8000 motorhome from an estate for $500.
Your best strategy as a buyer is to not be looking for the "best deal" in terms of how much below some arbitrary asking price. Best strategy is to know pretty much what you want, know what the value of that is to you, and seek it out at that price or negotiate to that price. If you can find it for less, great, but don't be passing something up because you can't get it for some percentage less than what was asked.
Consignments particularly, that price could already be as low as the seller will go. Consignment dealers will often let sellers start high, see that the unit is not selling, then work prices down in Dutch auction style. When the asking price hits market value, a unit that has been siiting unsold will disappear quickly. I've lost the chance to purchase two RVs and a tow vehicle offered at fair prices, simply because I couldn't decide quickly enough.
How do you know when the price is right? You study the recent sales in your area of the same or similar things, just as you would for housing. For vehicles, however, you also have an option to look elsewhere, and if another market is selling lower, decide whether the lower cost is worth your trouble to buy there. I tend to put some limits on this, will not look at Dallas-Fort Worth, Oklahoma City, Kansas City, or Wichita, but won't be reaching out to Chicago, Atlanta, Phoenix, Seattle, or southern California unless seeking something really hard to find, particularly since the higher cost of living in those areas tends to inflate the price of everything.
