Booking money changes the relationship between you and a developer, so verify everything before that moment, not after. Start with the approved design: ask to see the RAJUK-approved sheet with the memo number, and match the number of floors on paper with what is being marketed. A surprising number of disputes in Dhaka begin with one extra floor that was never approved.
Second, check land ownership documents: the mutation khatian in the developer's or landowner's name, the up-to-date land tax receipt, and the registered deed of agreement between landowner and developer. Third, ask for the soil test report and structural design certification. A serious developer will show these without hesitation.
Finally, read the allotment agreement draft at home, not at the sales desk. Look for the handover date, the grace period, the compensation clause for delays, and exactly what "utility cost" and "additional work" mean. If a clause is vague, ask for it in writing. At KinOn Holdings, we hand buyers a single document folder containing every approval - and we would advise you to expect the same from anyone else.