You need not worry about the offer which is made by anyone. Ask yourself what you deserve and show the person you are capable enough.
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Send them a "good answer" either to correct the mistake or explain that in this salary a peon is not available.
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If it is claimed that it was a typing mistake; then one can assess the "quality" of the firm also how they present before the public.
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There are many unorganised clients who don't value the services of a qualified chartered accountants and I surprise why qualified chartered accountants fear to lose the work.
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The answer is : They lack in their professional skills.
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Professional skills don't include only knowledge about the subject but GREAT PRESENTATION OF THE KNOWLEDGE BEFORE THE CLIENTS as well which may include -
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To create fear in the clients what will happen if they don't follow the rules and regulations applicable to them.