Question Summary:
Is it permissible to outbid someone in an auction?

Question Detail:

Is it permissible to outbid a Muslim. If he has made an offer in an auction or privately, then is it allowed to outbid him for something  he was expecting to to buy. He may be in great need for it while the one who outbids him may not be in need for it.. It is the same with marriage. If a Muslim brother has made a proposal for marriage is it allowed for another to go and make proposal to the same girl?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
It is permissible to outbid someone in an auction.[1] However, in a normal transaction it is impermissible to place an offer of purchase for an item that another buyer has already negotiated with the seller.[2] Similarly, it is impermissible to propose to a girl who is proposed to.[3] Yes, if the girl’s family shows disinterest in the proposal, then one may make a proposal.     
And Allah Ta’āla Knows Best
Hisham Dawood
Student Darul Iftaa
Chicago, USA 
Checked and Approved by,
Mufti Ebrahim Desai.
Daruliftaa.net