were learning about affirmative/negative usted/tu commands and on the model it says "Tenemos pelo sucio. (el perfume)" and then the answer is "no lo compren" why compren, why not compre?

2 answers

Look at the endings.... Is one singular and one plural? Is tenemos singular or plural?
It will be that easy = singular or plural.

If you are speaking to one person, saying don't buy: no compres (tú) and no compre (usted)

If you are speaking to more than one person = no compréis (vosotros) but no compren ustedes)

That's it for the negative, HOWEVER the affirmative command for tú is just like the 3rd-person singular of the Present tense.

Compra (tú) but Compre (usted)

Comprad (vosotros) but Compren (ustedes)

Sra