I like it a lot.
'Piace' — 'PYA-che'. The 'ia' glides quickly — don't separate it into two distinct vowels.
After trying something on or looking at an item. Signals your interest to the assistant without fully committing to a purchase.
'Piacere' works inversely: the subject is the thing liked, not the person. 'Mi piace questo vestito' = This dress pleases me. Singular item → 'piace'; plural → 'piacciono'.
Mi piacciono molto questi.
I really like these.
Plural: 'piacciono' for multiple items
È bellissimo.
It's beautiful.
Commenting on the item itself
Non mi dispiace.
I don't dislike it / It's not bad.
More reserved — Italian understatement
Italian shop assistants often comment on how items look on you — 'Le sta bene' (it suits you). This is meant genuinely in small boutiques, though in chain stores it can be a sales technique.