Zero-knowledge proof for the product of additive Paillier ciphers
Assuming entities do want Bob to decrypt the sum, but not be able to decrypt individual ciphertexts: enitites would send commitments to plaintext to Bob while sending ciphertexts to Alice. Commitment scheme should be additively homomorphic such that Bob could open the result (over commitments collected) with plaintex decrypted as verification. This would prevent Alice from manipulating ciphertexts collected (assuming honest entities).

Please note plaintext is not an integer in Paillier scheme modulo $n^2$, but a ring element modulo $n$.