First of all, a good agent will go thru the entire clause in the OTP in front of the seller and buyer. In this case, I suspect both seller and buyer's agent just allow both party to sign and very brief explanation. I always brief them especially the consequences of withdrawing sales from seller and buyer before the signing of the OTP.
The seller's agent should advice the seller to obtain the HLE from HDB or to obtain the In Principal Approval (IPA) from the bank first in order to proceed the marketing of the unit. A good seller's agent will assist the seller to check on the eligibility to sell, financially advice after the sales and buying another unit making sure that seller is fully understand with the process before marketing. Buyer agent only mistake for this was during the signing the OTP, he should add those important clause that miss out by the other agent that present the signing of OTP. But when seller withdrawer of the sales, he might not fully understand the losing ground. What i mean the seller's agent is fully responsible.
During this kind of situation, there is no need to pay any comm to buyer at all.