'Deal in' is a common phrasal verb that means to engage in a specific type of trade or commerce. However, there are several synonyms for this phrase, including 'trade in', 'dabble in', 'sell', 'buy and sell', 'participate in', 'engage in business' or 'specialize in'. 'Trade in' implies the buying and selling of something, while 'dabble in' and 'participate in' suggest a less formal association with a particular field. 'Sell', on the other hand, suggests a focus on the selling of products, while 'buy and sell' can involve both buying and selling activities. 'Engage in business' and 'specialize in' imply a professional or specific knowledge of a particular industry or field.