re: Applying for a job at a place where you do business

It's frowned upon or more accepted in some industries relative to others. For example, in construction, it's prett much an established fact that many of the workers working for the general contractor performing maintenance on a plant can end up working for that plant directly. Many construction companies are pipelines for jobs with various chemical companies and refiners. With construction laborers, it's even more ubiquitous. People change companies with every job. If they work a maintenance job at the same plant for years and their company loses that contract, a large percentage of those employees will stay behind and work for whomever takes over that contract.