You are assuming that the rows in the tbl_Party table will be in that orderly manner. No, it does not work that way. That is not how the tables in a relational datebase are designed. You should start re-designing your table(s).
Based on the little information that I got, I did a quick draft as follows for your reference:
table: patron
patron_id (primary key)
patron_name
[other fields]
table: seller
sale_id (primary key, foreign key to sale_id in sales table)
seller_id (primary key, foreign key to patron_id in sales table)
[other fields]
table: buyer
sale_id (primary key, foreign key to sale_id in sales table)
buyer_id (primary key, foreign key to patron_id in sales table)
[other fields]
table: sales
sale_id (primary key)
asking_price
offered_price
concluded_price
[other fields]
You should read more on
Relational Database Design[
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