Physical is similar to Natural. Natural is a synonym of Essential. 
Auction is a type of Sell. Auction is related to Benefit. Benefit is related to Bonus. Bonus is related to Reward. 
Physical <--SimilarTo--> Natural <--Synonym--> Essential 
Sell <--IsA-- Auction <--RelatedTo--> Benefit <--RelatedTo--> Bonus <--RelatedTo--> Reward 