There is a saying that goes like this " if you can sell a pen , you can sell a house. Selling is selling ". do you agree?

I don't think that this is true for all products/services. In otherwords, can you sell a plane if you can sell a pen. You need to understand the productservice your are selling, its customers, it markets, & it competitiveness.

Yes that is true. And if one have a capability to sell a pen professionally then he can surely sell a house as well. But to sell a house he may need to dig deep in the same market to sell a house.

With the proper product training a true salesperson can sell anything while the opposite is not true. Selling is an art not a science. and salespeople are a different breed!

Such sayings are not applicable among professional sales people.

Selling is art... a salesman  on roads also sales his product ...easily..Don't need a degree & other criteria for that..

Agree100% The one who have the talent of sales, can sell what ever !