Most of the big mistakes candidates make during negotiations they might never even realize.
One of the biggest mistakes candidates make is believing the recruiter is their advocate at the negotiating table.
The recruiter works for the employer, not you.
Yes, most recruiters are nice people and they are helpful in many ways. This is not an indictment of recruiters in any way. I was one for years. It's simply a wake up call for candidates to realize that the recruiter is loyal to the one who pays them. This is as it should be.
Everything you share with a recruiter related to your situation will be shared with the employer. Your background situation, the other opportunities you have in the mix, your enthusiasm about this job and location, your willingness to relocate and travel, and definitely the details of your financial position and desires are all shared if you divulge any of it.
When I was in recruiting I was amazed at how much personal information candidates would share, without even asking, that negatively affected their negotiating position. It wasn't rare. It happened all the time.
Work with recruiters. They are good sources of job leads. But recognize which team's jersey they wear.