These fields should be easy to search. Some dealers find it useful to have a field telling how large a purchase a customer is likely to make. Such a field should be handled discreetly. Some people would be offended if they discovered they were so rated. A disgruntled or dishonest employee could do damage with such information.
Some databases permit password protection of specific fields, but such protection can be defeated.
Anything as complex as a customer file needs a comment field. This should be searchable too. Again, consider the need for password protection or at least for discretion in the wording of the comments. You never know who might read them. Links to an inventory history file identifying past purchases by a customer are invaluable.