Possible Clues:

• After sales talk, study's done up with decorations
• With a decorative repeating design
• Tender tap (anag.)
• What isn't plain, in the material sense, is a set of instructions for writer
• Girl reportedly twisted and dotty?
• According to plan, glib talk has surprising end
• Fancy study being held up after sales spiel
• ... talk to Edward, with a design
• That's not made it plain
• Like tattersall