Been thinking far far to much about this.
Now a Selkie would be a fool to just randomly start dropping something as precious as their coat at a potential lover/mate when courting. As there's always a risk of someone truly stealing it.
So first they start with smaller trinkets, and less important things as a sort of test of character, see if they'll return even that.
(Assuming they don't already know well the one they are courting then they may just skip straight to leaving their coat.
After leaving various other small less precious things is the first drop.
The first time dropping her coat marks a way of showing interest, and sort of judge character. Will they return it, leave it or try to take for themselves? never walking far from where they dropped it given how precious their coat is.
A subtle sort of "oops I dropped it" type moment where they feign not noticing and start to take a few steps.
if the prospective lover reciprocates and makes to return the coat the selkie may again (at a later time) drop/leave their coat behind continuing the courting, this time while actively leaving it behind to be returned
On the second drop they'll actively allow themselves to walk away back turned without leaving altogether. This allows a layer of trust unable to see what the other is doing. Will they steal it? ignore it or bring it to them.
Again should the prospective lover reciprocate in kind and return the coat the courting continues.
Of course between Coat drops there's plenty of time for thr getting to know - some Selkies will do it on consecutive days but only if they are THAT sure.
The third time they will "forget: to take it with them and purposfully leave their coat behind at their lovers home/ with their lover. Like staying over night and then quietly leaving at the dawn and not taking it with.
Or otherwise seemingly 'leave it behind ' somewhere to be found. Commonly it'll be carefully folded and place upon rocks or someplace else where it will be obviously found
The fourth and final time typically a Selkie will give their coat to the one they've been courting !and if it's gotten this far safe to say it's a sure thing.
After giving the coat will ask to meet at the shore and to bring the coat. Where upon returning selkie will ask to put their coat on them.
3 times the coat lost and thrice was it returned. My coat I gave to you as I would my heart and love now I ask you, would you return my coat as you would your own heart and love?
This time instead of handing the coat the coat is returned by placing it on the selkie themselves. Or for a pair of Selkies swapping coats (like exchanging rings)
For a non Selkie being courted Selkie may intern place a part of their coat over their lover or something.
It's the 4th exchange and return of the coat that well seals it
Now important to note all though some amount of fae magic/logic is involved. If the one being courted should not share these feelings- and you know are just a nice person they're not locked into wedding the Selkie / can reject them
When it comes to Selkies themselves there's never any confusion since they know when another is courting - and frequently is seen as sort of a lovers game more then anything.
Really it's the number of times that means more then the how. As well as the intent behind the drop.
And it can't be all in one day