As a hiring manager this is simply not a big deal. Any employee can leave at any time for any reason. I dont see anything wrong ethically with calling to turn down the original position. If they are truly good people they would recognize that it could be better for your career and be happy for you.
If it isnt truly better for your career, then they will have the opportunity to explain why or sweeten.
The only time I get upset is if someone leaves in the middle of a project without enough notice.
Have you tried hiring during a college cycle? There's a pool of people, and in general the people you want to hire will accept a job offer before may.
It is especially frustrating if you have already planned and allocated resources to hiring a candidate, and then found out that the candidate rejected an offer. At that point, some employers actually call the school and complain, and that's definitely something bad for a college grad .
Note: Again, its a general statement: there are point examples of very sharp college grads deciding to search for jobs in april, but for the most part the better people accept offers earlier in the year
With regards to your ethical query, what happens if the tables were turned [i.e. company offered and then rescinded the offer months later]? Would that be ethical?
It isnt very nice, but Im sure it happens. We would only do it if business circumstances forced us to do it (not because we found someone better). If at all possible we would pay them a "severance" probably around 2 weeks of salary.
It depends on the project. I would hope that our people give enough notice that their leaving doesnt impact a release cycle by giving us enough time that we can put someone else on the project to transition to. Usually 2 weeks is sufficient.
If it isnt truly better for your career, then they will have the opportunity to explain why or sweeten.
The only time I get upset is if someone leaves in the middle of a project without enough notice.