If you are selling to a reseller, then pushing makes sense.
For end users, they hardly every go through the trouble to open a new account, they will stick to the registrar of their choice.
Saying you wouldn't sell a domain if they don't set up an account at your registrar just simply doesnt make sense, nor is it professional.
You need to unlock the domain, get the EPP code, tell them to initiate a transfer after you have given them the EPP code.
You will then be notified by your registrar and you will need (in most cases) to agree to the transfer.
For large sums, it is best to use an escrow service.
If you know or trust the other person, or, have already received payment, then just go ahead and unlock and give them the EPP code.