As a broker of hard and private mortgages like Jeff, I agree with his assessment...up to a point. Labeling a second lien as "never safe" is unfair, though yes, of course they come with MUCH more substantial risks than a first. Still, I've brokered many successful second liens for my beneficiaries on flip properties, and they've been very happy with the result.
However, there are a number of issues with this particular deal, which should lead you to ultimately reconsider:
$60,000 on a $700,000 purchase is in fact a very small estimate unless they are purchasing an REO or Short Sale and buying at a major discount already...so the $60K will end up being simple cosmetic stuff. That does happen (I see it all the time), but almost never from a first time flipper. The experienced developers get those deals. Jeff S already focused on a few of the other issues, but left out one big one every private lender should consider...
...even if you went forward with this deal, you're not getting enough of a return for the risk. Not nearly enough. Second lien holders top out at 65% (maybe 70%) CLTV of AS IS value, and those interest rates are often above 12%. What this borrower is asking of you is not to be their second lien holder...they are really asking you to be their partner on the deal. And as a partner, you should be paid profit participation plus a "pref" interest rate. Simple 12% monthly interest return for your gap financing is quite honestly a slap in your face.
Bottom line...nope.