why use the plural form sellers and buyers instead of seller and buyer as signing parties in a sales contract?

Question by Joseph Tu: why use the plural form sellers and buyers instead of seller and buyer as signing parties in a sales contract?
e.g. This contract is made by and between the Sellers and the Buyers；Whereby the Sellers agree to sell and the buyers agree to buy the undermentioned goods according to the terms and conditions stipulated below and overleaf.
In fact, there is only one seller and one buyer here in the contract. why should we use plural form buyers and sellers ?

Best answer:

Answer by look at yourself
Actually the only certainty for either of you is there are only two signers of the contract. The number of buyers and sellers could include a wide range of possibilities.

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