We’ll, conventional posts tags are not user specific. They are site wide. You could use a custom fields text field to allow users to add comma delimited words (tags/keywords) but they would not be truly tags and there would not be a way to links to those keywords.
Again, you could use categories. Create a parent category called “tags”. As children categories add such as “Lawyers in Brickell Dr Miami” or “Best Lawyers in Miami” “Injury attorneys in Miami” categories. You can assign them as you normally would since each entry can be assigned more than one category. This way you can link to and filter by the categories. You could even use the Split Categories addon to split the “Tags” category into it’s on metabox so they are separate from the other caegories.
Hope this helps!