I ship bettas/ guppies all the time.
Just make sure you double package them put plenty of impact absorbsy stuff like packaging peanuts, styrophome, or bubble wrap around them. If its cold out that you line it all with newspaper and wrap your heat pack in newspaper as well, also make sure its not directly touching the shipping bags it can get too hot then.
Last but not least make sure your heat pack will last the amount of time its going to take to ship from you to them. My 72 hour one usually lasts 3-4 days for me.
I also breed and often sell guppies, I have the following strains.
Double Dark Blue Moscows, Half Blacks, and Albino Blue Topaz.
If your interested in purchaseing a pair or trio just pm and i'll let you know what I currently have ready to sell. Or if you just want to see pictures pm me.
Members get a discount!