I offer a certain part for a car, modified to overcome a well known issue. I'm offering the modification as an exchange via the post, at no more than the bare cost of the materials to carry out the modification, plus the cost of postage.
To avoid the car being off the road whilst the part is away being modified, I send out the modified part first, then await the return of the old part so it can be modified for the next person. To keep costs down, for both parties I insist they pay by a paypal payment as a gift. Basically I'm doing the job as a favour to members of a car club.
The problem is that I charge £7 for the modified part, yet to buy a new part which then needs modification costs £15. Not very often, someone gets the part and then doesn't bother returning the old part to me - which then leaves me out of pocket to the tune of £15 to buy a replacement.
So I was thinking to start charging a £15 refundable deposit on the old part.
My question is - If i were to ask for two paypal payments (£7 + £15) and were to bounce the £15 back once the old part has been returned, are there any extra costs involved in bouncing a payment back to the sender, for either me or the sender? Is there any time limit on bouncing a payment back to the sender?