Someone rang?
First, if you are new to leasing in general, I would read up on all the moving parts and read some of the threads on this board. You need to understand all of the moving parts before you can try to understand loaner leasing. Leasing is not for the uninformed, let alone trying to hack leasing on new or former loaner cars.
Second, Short answer is this: the loaner leasing game in Seattle is extremely difficult, but not impossible, if you have time, patience, and flexibility. It took me 4 months before I found my deal.
As @empirestate outlined, former loaners are cars the dealer used as courtesy cars or demos that have miles on them, but can be sold at a pretty significant discount due to the fact that they could have several thousand miles. You can search the forum for ways to identify a former loaner, but here in WA you can see in the carfax that it says “Dealer took title while in inventory.”
BMW loaners can be leased with new car rates and incentives, with the exception of OL code incentives and Fleet, if they have less than 5000 miles on the odometer. The residual value is reduced by $.25/mile for every mile over 500 that the car has on the odometer.
Mercedes loaners can be leased with new car rates and incentives if they have less 10,000 miles on the odometer. The residual value is reduced by $.20/mile for every mile over 3000 that the car has on the odometer. You can also still put down multiple refundable security deposits (MSD) to reduce your overall interest rate.
Here is the tough part:
(1) I highly doubt you will find a BMW loaner in your price range in the PNW. Just my experience over the last few months.
BMW Seattle is not an aggressive dealer in terms of deals. They generally do not discount their loaners that much. Occasionally you can catch a deal at BMW Bellevue, but as an autonation dealer, they do not haggle and will mark up the money factor. Therefore, you have to wait until they publicly reduce the price to a number you like and then you can go in for the kill.
You may have better luck down in Portland with Kuni or BMW Portland, but even they aren’t that aggressive in terms of discounts.
(2) Mercedes is a similar story. MB Lynnwood and MB Seattle are not volume dealers and will not discount. Your best shot in Seattle Metro is at Mercedes of Bellevue - they will discount their loaners pretty aggressively if you wait long enough - I ended up with a great deal from there, but there was no haggling at all except on the money factor. Your best shot for a quick deal is probably down in Portland with Wilsonville Mercedes or Mercedes of Beaverton. My thread is around here somewhere so you can read the details.
Happy to help with specific questions. You mentioned an Audi A3 in your PMs to me - Audi in general just does not lease competitively.
One last thing - lease support for 2017 BMWs and Mercedes could disappear at any time now. Move quickly if you see something priced competitively. If you get a quote from a dealer, you’re welcome to post it here and we can help you dissect it - just make sure you post all the relevant components of the deal (MSRP, Sale Price, Rebates, Term, Mileage, Money Factor, Residual etc.).