You need mortgage pre-approval in order to go into contract, but you are not committed to getting a mortgage from the bank that gives you pre-approval. You can and should shop around for the best mortgage rate after going into contract.
Negotiating interest rate is more important than negotiating price. Get as many mortgage offers as you can, and bargain them against each other.
Small banks often offer better mortgage terms than large banks.
Ask to follow the home inspector around, and ask them questions.
Read the contracts carefully. No one else will care as much as you.
Check the HOA / condo finances. Read the board minutes. Make sure they are not psycho.