This aspect (and many others) of contract law is applicable in the US and various countries of the EU.
can they renege after the candidate has begun their journey, thus
saddling the candidate with the travel cost?
No. The company would incur breach of contract.
There is no need for a formal contract. The candidate only needs to prove that the company agreed (in writing, orally or clearly through its conduct) to cover or reimburse those expenses and that this elicited a meeting of the minds.
The agreement would be void if the candidate incurred the expenses despite knowing (via timely notice) that the company changed its mind.
Likewise, if the candidate lied on his CV, the contract (here, the company's agreement to cover the expenses) would be voidable by the company, since the candidate's intentional misrepresentations preclude the aforementioned condition of meeting of the minds.
--Edited on 1/18/2019 to add ...--
Per suggestion by @KRyan, the aspect of void or voidable contract is expanded. But first, two disclaimers are pertinent:
- We need to be mindful that many of the follow-up concerns are either
premised on or inspired by the situation described in the underlying
Workplace SE post. These are somewhat beyond the scope of this Law SE
question but addressed nonetheless, given their relevance as well as the OP's & audience's
- The follow-up hypotheticals [in this Law SE question] and
clarifications thereto neither speculate nor pass judgment on the
stranded candidate who asked on Workplace SE. The Workplace SE post
reflects a company's breach of contract. The subsequent comments here about fraud
hypotheticals are mostly derivative inquiries beyond what
is described in Workplace SE. In particular, we do not assume
whatsoever that the stranded candidate committed fraud.
can the contract be voided on the spot like that without first
proving in court? As it seems like it grants a rather "vigilante"
justice power that is open to abuse, since effectively the
"punishment" (cancellation of the flight and thus inducing a rather
serious physical situation) is administered before any due process has
been afforded the one accused.
Yes, it can be voided on the spot (aka sua sponte).
"Vigilante" justice denotes a self-attribution of punitive powers that exclusively belong to the state/government/court, whereas a party's voiding of a contract is the act of foreclosing his losses/exposures with respect to a contract that de facto never existed (such as when that contract was induced by fraud).
I agree that unfortunately that is open to abuse: As a pretext to actually incur breach of contract, a company might allege that the contract was void. That is why (if taken to court) it will be the company's burden to prove that (1) it reasonably relied upon a candidate's representations (2) which were significant and blatantly false (3) given the candidate's knowledge that his lies contravened the job's core requirements.
That can be quite burdensome. For instance, is the company handing out airfares without first conducting some competent corroborations about the candidate's credentials/skills? If so, one can hardly concede the company's allegation of reasonable reliance. The resulting finding would be that the contract was not voidable by the company, and thus that it is liable for breach of contract.
Also, belatedly "informing" the stranded candidate that the company "is going in a different direction" falls short of evidencing that the contract was voidable. That applies even if the candidate performed very poorly in the interview or screening process.
Given the hardship imposed on a stranded candidate, a company has to be morally and legally very judicious about its method and timing for "going in a different direction".
But absent any representations or [company's] bylaws to the contrary, a company generally does not have the obligation to afford due process to a candidate. The court is the entity with an obligation to enforce due process as provided by law (although many of us in the U.S. have repeatedly experienced the courts' disavowal of due process).
--End of edit on 1/19/2019--
a binding agreement requires both sides to give something
Here, the candidate's consideration is his time and effort to accommodate the company's interest in assessing the candidate's profile at a location that is convenient to the company.