Do you have this in size M?
'M' is pronounced 'emme' in Italian — EM-me.
Use when you have already chosen an item and need to check if your size is available. Point to the item or hold it up as you speak — this removes any ambiguity.
'Avete' is the second-person plural (voi) of 'avere' — used to address the shop. 'Questa' (this, feminine) refers to the item you are holding. 'In taglia M' means in size M. Letter sizes (XS, S, M, L, XL, XXL) are internationally understood in Italian shops.
Avete questa in quarantadue?
Do you have this in forty-two?
Uses Italian numeric size.
C'è questa in taglia più piccola?
Is there this in a smaller size?
Relative sizing — when you don't know the exact number.
Esiste in taglia XL?
Does it exist in size XL?
Checks if the size is made at all.
Italian fashion boutiques often have limited stock per size, especially in smaller shops. If your size is not on the floor, always ask — stock is frequently kept in the 'magazzino' (stockroom) at the back.