1) Which sentence does not make sense?
2) Do the meaning for the sentences correctly?
If a customer is sold bad product, we will lose that customer.
If bad product is sold to a customer, we will lose that customer
Meaning of sentence 1:
If a customer receives bad product, we will lose that customer.
Meaning of sentence 2:
If we sell bad product to a customer, we will lose that customer.
I don't see any difference in meaning in the two sentences at all.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
I think your confusion comes from the apparent ambiguity about what is sold - the customer or the product.
1. If a customer is sold ...
2. If a bad product is sold ...
What you have done is chosen a ditransitive verb (to sell) and put it into the passive voice. The originals might be:
3. If we sell the customer a bad product ...
4. If we sell a bad product to the customer ...
In both cases, the direct object is 'a bad product' and the indirect object is 'the customer'. The two objects share the same verb, and the subject "we" is left out of your original passive clauses.
The irregular passive - probably on account of its brevity - interestingly, tends to be the more natural of the two in most cases.