1. If a person has made an offer to purchase and the seller is inclined to concluding the deal, then it is impermissible for anyone else to make an offer over the offer of the purchaser. This has been prohibited in the Hadith. However, if the seller is not inclined to the offer, then it is permissible for others to make an offer to purchase.
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: لا يسم المسلم على سوم أخيه. (صحيح مسلم رقم 1515)
Hazrat Abu Hurayrah (Radhiyallahu Anhu) reports that Rasulullah (Sallallahu Alaihi Wasallam) said: “A Muslim should not make an offer to purchase over the offer of his brother (i.e. in the case where the seller is inclined towards concluding the deal).”