Is there a problem of accepting a job offer (signed contract) during the 3 weeks? 9 days?
In case it matters, it would be a full time salaried job. The business owner seems to be Jewish (not 100% sure) but unaffiliated.
It is permitted to sign the contract even during the nine days. The reason for this is, that although in general it says should minimize our business dealings during the nine days, The poskim say that the minhag nowadays is that we do business, because it is all considered for our needs, especially for you where it is means your whole livelihood, therefore it is permitted.