Make sure that your lender is aware of the $72,900 to $180,000 leap in value.
The seller may not be able to sell to someone who requires the scrutiny of loan underwriting - the leap in value in 9 months may be too much money for a bank to enable.
Ask the seller if they have a day to day logbook for the job. Ask them for every material receipt and labor invoice. Ask them to justify the asking price as if this were a "cost plus" build that you contracted yourself.
If they are attempting to make more than a 40% profit, then watch out. That means that they must have put at least $30,000 or so into it.
If their labor and materials are legitimately accountable, but their work is not so good, then question their profit margin.
If $180,000 is commensurate with immediate comparable, appraisable like-kind property values, then go for it.