'Antiques Roadshow' guest struggled to speak after hearing the value of her father-in-law's guitarThe owner of a decades old Martin D-18 guitar couldn't believe it was worth five figures. The owner of a 1938 Martin D-18 Guitar had no idea how popular the item was in the market until the show's expert, David Bonsey, explained it to her. Screenshots showing the guest's reaction to the appraisal (Image source: YouTube/Antiques Roadshow)Explaining the history behind the guitar, the guest said, "This was my father-in-law's guitar. So we call that 'advanced bracing,' which makes it a more valuable guitar," Bonsey added. More on Market Realist:'Antiques Roadshow' guest surprised at $30,000 appraisal for heirloom — still refuses to sell it'Antiques Roadshow' guest stunned after hearing the value of 1959 painting she received as gift'Antiques Roadshow' expert was left 'emotionally struck' by rare chalk drawing from the 1770