I would suggest buying through an authorized dealer (AD) or an established grey market dealer such as davidsw already mentioned, authenticwatches.com, chrono24 and others rather than purchasing used from a private party. Watch dealers may have a used verion of what you are looking for which could save you some $$
Once you get a feel for what the grey market dealers are selling the watch for, I would contact some ADs and see if they will discount to match or come close to grey market pricing. I once purchased a Breitling through feldmar watches in Los Angeles https://feldmarwatch.com/ and they discounted enough to match grey market pricing. Also they shipped to me out of state so there was no sales tax. On a Tag, I'd expect to get a discount since they seem to be available and not on allocation to where the market price is above MSRP like Rolex is.