Hi Jesus,

Thank you for contacting Mearto with your appraisal inquiry.
I am 99% certain this is not the work of Robert Theer for at least two reasons: the signature is quite unlike any documented to his known examples, and the quality of the portrait is not nearly as detailed and refined as one would expect to see in his portraits. For the sake of this appraisal, and barring additional information that would point to a reasonable attribution, I would call this "Continental School, 19th Century" and I've evaluated it based on its similarities in size, medium and subject matter to other works similarly auctioned.
Based on the photos and information provided, and subject to examination, this is:

Continental School, 19th Century
Portrait of a Scholar
oil on canvas
24 by 36 inches, in a giltwood frame 33 by 45 inches
signed somewhat indistinctly "RoberThee"
CONDITION: This portrait appears to be in generally good condition; value assumes this has not been relined, restretched, in-painted. repaired or revarnished.
PROVENANCE: Acquired at a flea market
$300-500*
*represents a fair-market value for auction purposes; retail or asking price may vary.

Please let us know if you have additional items to appraise, or questions/concerns, and thank you again for using Mearto.
~ Delia