Hello...
4.9 is a good engine...a bit underpowered IMO when compared to what else is available for the same money.
He offers several clean Cadillacs so it looks like he's not new to this.
The bluebook value is $5,175 (clean, reliable vehicles are always worth more).
Ultimately, a thing is only worth what someone will pay for it.
PS...it IS a fake (Imitation) convertible top-
sometimes referred to as Carriage. Also Ragtop.