Don't get me wrong - I'm not suggesting that you lie if this is, in fact, the case. However, if you are like many business owners you are also playing some roles in the company that could be delegated, you likely are spending some of your work week devoted to more personal projects, and there may actually be people with strong experience out there who could be hired who are more efficient and effective than you are. The problem with selling how important you are to the operation of the business is that a business buyer may have second thoughts about whether they can successfully operate the business without you, whether they will they be able to find an eventual replacement for you, and if they will need to significantly increase the budget for replacement staff which increases their projected expenses and thus, lowers profitability and value.
Maybe exaggerating your importance helps you negotiate a higher pay rate for your 1-2 year transition, but what does this mean for the valuation of your business? If the market rate for your position is $150,000, but a buyer believes that they will have to hire two $100,000 employees to replace you, that means they will have $50,000+ in greater expenses and lower profits. That additional $50,000 profit if included in valuation calculations may mean a difference in value of $150,000 - $300,000 in business value.