If I may play devil's advocate. I understand markets shift and in this case, it appears to have shifted away from OP's favor towards the dealer and that's why they're not honoring the 3% discount and is now charging $5k ADM. On the flip side, many folks purchased the car during COVID with many putting deposits at the beginning of covid (March 2020) and the market moved drastically in the customer's favor during that time. I suppose people could have gone to the dealers and asked for further discounts on the cars as supply/allocations started flooding the market, inventory built up on showrooms, and covid seemed to only be getting worse and worse in the early days of covid. Funny thing is, I recall a RLister asking about going back to the dealer and asking for more discount since the market was getting softer on big purchases especially luxury purchases and he basically got blasted on RL with many people saying how would he like it if the market shifted back to the dealer's favor and if he would appreciate it if the dealer then turned around and reneged on the aggreement and then charge an ADM?

Personally, if the (gentlemen's) agreement was for 3% off, they should honor it. Otherwise, Porsche of BH should have made an agreement to say something like due to current market conditions, we're willing to offer you 3% discount off MSRP but this is subject to change based on market conditions as determined at the time of delivery. This would have been stated up front so that the customer knows that there is a chance that the 3% discount might not stick if market conditions shift back to the dealer's favor.

That is how I would prefer business be done. Call me old school but my dad taught me that your word (and honor) is supposed to mean something.