Answer: Option 1. are
as far as I know, these clients are used to high standards services and they won't settle for less.
Step-by-step explanation:
option 1. are is correct because here high standard of services is plural.
were would not be used because it is a verb be past tense and is used with the first and third plural subjects as well as the second person.
be would not be used because it is used to create passive and continuous tenses. The correct form of be, present or past, followed by the present participle is used in the continuous tenses of major verbs (or -ing form). The proper form of be is followed by the past participle in the passive form of a primary verb.