In a word... YES.!!!!
Does the elderly gentleman need the money.??? Then offer to pay him more... An early Rockola carbine that has never been rebuilt... is worth beau coup more money than the price he has discussed with you...
If at all possible, don’t take advantage of him. It is worth far more than $400 and he may not know it or is desperate for funds. If you can swing it, I’d recommend paying him a fair price.