If an employer asks me the details of other job offers - (company and salary offered), should I always tell them?
Once I had been asked both and I gave them that info. What happened next stunned me. The interviewer asked me if I could show the job offer letter. There was no "confidentiality agreement" protecting that letter. So, I opened up my mail on my phone and showed him the e-mail anyway. I guess he was only trying to find out if I really had a job offer.
I am not really sure if this was the right thing to do. I guess it enabled me to negotiate better with them. But, I did not get that job in the end.
Confirming when you have other offers or negotations going on is a) an honest answer and b) may strengthen your position ("Other people also value this person").
Showing the job offer letter or divulging the name of the other company is a break of integrity. You don't disclose your negotiations with party A to B or vice versa. (Also, should you do that it can be interpreted as you not having integrity/not being thrustworthy). There does not need to be a 'confidentiality agreement' for that. The interviewer asking for the letter was improper behaviour.
Most of the organisations asks about whether do you hold an offer and value of the offer for the following reasons
To figure it out whether they can affordable you or not. If the value of the offer that you hold is more than their budget they can not afford you. In that case they will consider other candidate. Most probably this might be the case with you.
To know the limits of negotiation. Based on the information they can realize how extent the offer will be negotiable. Definatly they have to offer greater than or equal the existing offer that you had or they have to show some justifiable reason if they would like to offer less than the offer that you hold on hand.
To figure it out how soon you can join. If you had already serving the notice period there are good chances that you can join very soon.
Finally it shows how valuable you are in the market.
However the reason behind asking about showing offer letter is to figure it out whether you are saying truth or not. I am not sure how appropriate it is, but some organisations will go based on proofs rather than just word of mouth. However my personal opinion is showing proofs to whatever we said confirms that we are trustworthy.