My first investment flat hunt: Pre-launch vs actual value

Since last Diwali, I'm seriously looking for an investment flat in Gurgaon. Builders like Bricksquare Developers Sector 17 mein pre-launch deals dete hain, bolte hain best price hai. But is it actually a discount, ya bas marketing hype? Matlab, pre-launch pricing vs open-market price mein kitna farak hota hai? Also, construction-linked payment plans vs upfront down payment pe spot discount— which one is smarter for an investor? Kya payment plan leverage kar sakte hain? Any advice on broker vs direct builder deals for better ROI?