There was a transfer of ownership for a property in 2017. The remaining balance was $37K. This was considered the purchase price. Is there capital gain to the seller?

what do you mean by remaining balance? remaining balance on what? what type of property.  who was it sold to? was it sold at fair market value.? was the buyer related to the seller?  how? as you can see we are going to need a lot more details on what occurred to answer your question.  it is possible that even after you answer these questions more information may be required.

here's a generality. the sales price is the sales price on whatever document there was for the sale.  the seller compares it to his basis.  (basis would include selling expenses)  a gain is taxable. a loss may not be deductible if it involves personal property not used in a business.  this could be a home, a car, etc.  even business property sold at a loss won't be deductible if sold to a related party.