Can't say we've found any particular type to be too unreliable as yet / in the past 2 years, but then you are dealing with up to 3 times the enquiries, bookings and work with your place/s as you can split yours up into 3 and be far more flexible than we can.
We did have a family book for Xmas this year last Jan and then decided to book a week prior in May for a Spring week-break / recce and to see how far it would take them to drive to Megeve to see friends who would be staying there at Xmas whilst they were at our place.
Unfortunately, May turned out to be an extremely snowy month (having had little snow the rest of the season) and they ended up being snowed in for 3 days as their hire car didn't have winter tyres or any snow chains (well, it was May). They then ventured out and made the trip to Megeve, which took them far longer than it would normally do due to the weather.
I think the whole experience was far too traumatic for them (new baby in tow as well) and when they got back they politely cancelled, saying they'd probably stay in Megeve - which I coudn't argue with and sounded a wise move. We had no problem booking Xmas again anyway, but I do sometimes get nervous when a party book for a recce visit, especially if it's in a 'shoulder' month when the weather can be changeable.
We've always called in balance & security deposits 8 weeks prior with 30% deposit at time of booking and not had any grumbles. I'm sure those who don't like those terms don't bother even enquiring, which is fine by me as I can't abide time wasters and I won't get into haggling / bargaining etc.
I did wonder if they'd grumble at the security deposit being taken so far in advance, with potential to earn us interest etc, but the only reason it's collected then is to avoid having to do three lots of different collections (+ the return of it) and therefore cut down on the admin a little. However, I shan't worry now that I've read how successful Margaret is at collecting the whole lot ! Hats off to you Margaret
Beanie