Consider the influx of rich people into your groceries market.
Consider the lower real prices of food in certain countries, in spite of low transportation costs (which should equalize food costs worldwide).
Consider that some think the influx of rich people, will raise their costs.
Consider that some think the influx of rich people will increase available wealth in the area.
To the point:
The balance of benefits and costs is determined by:
Costs: how much does the person buy locally to consume? This is the consumption that you bear. To you, It reduces quantity of goods available and raises prices, marginally.
Benefits: How much does the person produce to sell locally? This is the productivity that you (generally probably) enjoy. To you, It increases quantity of goods available and lowers prices, marginally.
It is possible for people to produce and export worldwide while consuming locally. The reverse is also possible. this of course, would affect the balance. Added to the balance of local/total consumption or production, is also the consumption/production balance. Someone who just produces and never consumers is only a benefit. Someone who consumes more than they produce, by debt or aggression, is a burden.