"Buy a delicious strawberry."
Translation:맛있는 딸기를 사세요.
사다 = to buy 살다 = to live
살다 is an ㄹ irregular verb. I suggest to learn irregulars firstly.
Potentially, but it wouldn't make sense here obviously. 살다 can lose the ㄹ for certain conjugations.
사요 is not the imperative tense, which means that it cannot be used as an instruction. It is only used to state a fact, so your sentence would translate to "you buy a delicious strawberry."
사요 actually is the imperative tense. 사세요 consists of 사- to buy + -시- (honorific marker) + -어요 (imperative ending).