I'd definitely look for any alternative to the Landmark, as they are total muppets, or at least think we are. 
Looking at a quick trip either end of the month or early next.  Checked Landmark and saw that they have a "Book 2, Get 1 night FREE" deal for July, which was quite enticing. Selected the dates, selected "Premium Corner Room" @ THB4,733 per night, which is pretty much standard pricing for that room, but a great deal when you're getting a 3rd night free. I hit "Reserve Now" just to check that it's valid and lo and behold, it's a bit of a scam. 
Night 1 = THB7,100
Night 2 = THB7,100
Night 3 = FREE!

So all they've done is total up what they normally charged for three nights (THB4,733 x 3 = THB14,199)  and then divide that into two nights. Scumbags. 

I use gmail. I haven't had email notifications for years. I can only log on by clicking on old PM email links. 

Answering my own question here… seems like a problem between the site and gmail (or at least some gmail accounts). I updated the email on my account here to a brand new yahoo email address and the notifications started flowing in. Now I can’t change it back to a gmail address though as the activation-email you need for that doesn’t come through either of course. It’s not caught in the spam folder, the messages get lost somewhere before Google deposits them in the mailbox  Problem with the smtp sender reputation of bangkokladyboys.net?

Interesting, I will bear that in mind. I do like the Mercure, I was very impressed with the front of house staff. 

I'm not sure why one would book through Agoda. I have an upcoming trip and checked both with Agoda and directly with Mercure. For the same setup (Deluxe King, advance payment, no breakfast) Agoda charges $138/night all in, Mercure charges $121.25/night all in. I've almost always found booking directly with the hotel a better deal than through any of the consolidator companies. I've also done the same comparison for another hotel I'm considering (the Samala Hotel on Soi 15) and Agoda is closer to the Samala direct price but still a bit more expensive.