Reviewing a Heimishe company is 100% Loshen Hara, the only way it won't be LH is if the particular business is actually stealing.
Bad customer service experience is totally relative.
For example, if I owned a restaurant , and had a couple of waiters, now you have a nasty customer, (admit, there are plenty of those) demanding a refund because the steak he ordered came out not the way he wanted, now this guy gets all nasty at the waiter which triggers the waiter ( which is only one out of a few) to respond a bit unprofessionally.
Now this guy thinks he'll get even with the Restaurant (Ltoeles hatziber) and post about it in this thread.
Who is he hurting, the non Jewish waiter, or the Jewish owned Restaurant?