A purchasing manager I worked with once years ago was quite skilled in always developing multiple sources and then working them to get the best overall deal. As long as you aren't looking for highly custom or one-of-a kind products it works, sometimes passively (you don't negotiate the price of milk at your grocery store directly, but you choose where to buy it), sometimes actively (like visiting two or more different dealerships when buying a vehicle). No matter what authorized dealership you buy your Sprinter from, factory service and warranty repairs can be had at any other authorized dealership you like. If you don't work multiple sources, then you are very likely to pay more as you have eliminated your most powerful bargaining tool, market competition.
I can't find the on-line source I read while getting ready to purchase my van (the writer was a master at the craft and involved five different dealerships), this subject has been discussed before on the Forum <
https://sprinter-source.com/forum/showthread.php?t=35845>. How far you are wiling to go while negotiating is a personal matter; your extra time/energy might not be worth getting another $200 off the deal, but might well be worth $2,000. The dealerships are highly skilled and they vastly outweigh most of us in terms of experience. Any deal they make is one that they can live with, no matter how much they try to convince you that they are losing money or not making enough money to feed their starving children at home, so pushing them just as far as you can is NOT being unkind, it is just business.
Remember to consider total cost of ownership as you negotiate price, but be sure to use real numbers in your calculations (i.e., a dealer may throw in an extended warranty, or free services plan, in which case you need to know the real costs of those items and not some inflated value that makes them look more valuable than they are). Beware the after-sell in the finance office for paint protection packages, etc. (do your own research, but my opinion is that such things aren't worth much, at least not with just a one-time application). And remember that anything a dealer does on their own may not part of the factory warranty (factory options installed ex-factory by an authorized dealer probably are covered, fuzzy dice hanging from the mirror obviously aren't).
Stay vigilant all the way through picking up your van; don't "accept" the vehicle unless it is the one you want/ordered and everything you can (reasonably) check out for proper operation is in full working order. Once you take it home, it is yours. Before you take it home, it is still the dealer's even if they say it has your name on it. One forum poster even had a dealer sell off his custom-ordered van to another customer before he could come in to get it, and then wanted him to be happy with a different van that was not what he had ordered.
Read everything, ask lots of questions, try to avoid making any assumptions that you don't explicitly verify by asking more questions. Playing dumb is generally going to work better than acting like you know everything already (and become afraid to ask a question because you don't want to look stupid). Buying a new vehicle is something many of us do only a handful of times in our entire lives; dealers do it once/twice a day all year long (even more if they do fleet sales) every year they are in business. You are buying it from the dealership, not the personable salesperson whose hand you shake.